Warning: Geeky discussion of space battle in different universes follows:
Well, in Star Wars, we see lots of crew-served weapons, even on the largest and most sophisticated warships. When we do see capital ships fighting, it’s usually at very close range, using pulse energy weapons. Fighters are usually of limited consequence to the larger warships, though they can act effectively in support of their own capital ships (for example, in Return of the Jedi two Rebel starfighters destroy an important looking structure (possibly a sheild generator, possibly just a water tower) on the Super Star Destroyer while at least one (and presumably more than one) Rebel starcruiser attacked it. Fighters can also be used for reconnisance and projection of force, allowing a single warship to reach out and make it’s presence felt over a wide area, sometimes with the homeship being lightyears away in another starsystem. We never see a dedicated starfighter carrier, presumably because hyperdrive allows for the possibility of any ship suddenly finding another ship at close range with limited warning. The closest we’ve seen on screen are the Venator Star Cruisers from the Clone Wars and Episode III, which contained hundreds of fighters in a large series of hanger bays in the foward half of the ship. The aft portion of the ship contained several turrets, each mounting multiple crew-served energy cannons (presumably Turbolasers, possibly a larger weapon discarded in later designs).
In Star Trek, close to intermediate range capital ship combat is the rule of the day, with each major fleet fielding it’s own large capital ships and multiple smaller warships. We have seen relatively small Starfleet fighters (themselves the size of Starfleet Runabouts, and consisting mostly of engines and weapons, with a small crew space in the front), launching group attacks against smaller enemy warships, using a miniturized form of photon torpedos. These were used primarily to harass the enemy ships, and appeared to have limited effectiveness otherwise. Ships might use torpedos while at longer ranges, but usually close to point blank range to engage with beam or pulse weapons. A number of tactics (including the use of cloaking devices or “The Picard Maneuver”) have been devised to allow a ship to get close enough to bring it’s energy weapons into play.
Most fleets appear to have a few large battlecruisers (Vorcha or Galaxy) a number of intermediary cruisers (K’Tinga or Excelsior, and a number of smaller, faster, disposable frigate type ships (Bird of Prey or Miranda). Each fleet seems to have a different distribution of forces, with the Klingons favoring small disposable ships, Starfleet mid-range cruiser type ships, and the Romulans obviously favoring large, powerful battleships (curiously enough, the Romulans seem to totally lack smaller warships). Transporters are also used in combat to beam boarding parties onto an enemy ship, sometimes to sieze or sabotage the ship, othertimes in order to kidnap/rescue individual personel or equipment onboard. Transporting is almost impossible if the sheilds are up.
In BattleStar Galactica (at least, from the limited amount of it that I have seen), the capital ship carries various types of heavy weaponry, but relies on it’s onboard fighter compliment for reconnisance, defense, and force projection. Depending on the version of the show you are watching, small fighters are capable of various degrees of damage to enemy ships (in the original version, Colonial battlestars were vulnerable to attacks to their exposed hangerbays, while Cylon Basestars could find their external weaponry picked off by the agile Colonial Vipers, in the new version, Cylon raiders are capable of deploying nuclear missiles, which can cause significant damage to a BattleStar if not intercepted). Both versions featured Battlestars having to retreat while their fighter compliment fended off attack. In the original version, Vipers could be (and sometimes were) left behind by their motherships as the BattleStars were apparantly capable of outrunning their own fighter compliment (though they burned fuel at a prodigious rate if they did so). In the new version, Viper pilots often find themselves racing to land on the Galactica at the last moment before she can FTL jump out of the area. When the Vipers find themselves in this kind of situation, they usually find themselves under enemy fire even while trying to land. This sort of situation generally wouldn’t happen in a current-day navy lacking in FTL drives.
In the Wing Commander universe, capital ships are designed to fight other capital ships, but also find themselves having to defend against bombers, which carry torpedoes (often with nuclear or antimatter warheads) specially designed to phase through the capital ships’ heavy sheilds to strike the ship directly. In order to defend against bombers, fighters have to be deployed. Heavy fighters are capable both of dealing with enemy fighters and smaller ships, light fighters are better suited towards reconnisance, medium fighters are a jack-of-all trades, either performing their duties adequately or poorly (but rarely ever performing them remarkably well). While cruisers and destroyers can launch and recover fighters, larger dedicated carriers are usually set aside for this task. Where it is not possible to purpose-build a carrier, smaller ships are often modified for the purpose (the Union Of Border Worlds fields a type of carrier constructed by attaching a hanger bay between two destroyer hulls) A carrier equipped with substantial heavy capital-ship weaponry (often accompanied by some sort of BFG) is referred to as a Dreadnought While the Kilrathi used Dreadnoughts throughout the last half of the Terran-Kilrathi War, the Confederation stopped fielding them in the late 2660’s. Some fighters and most bombers are FTL capable, allowing a carrier to launch attacks into neighboring star systems without itself having to leave the system it’s in.
The fact that FTL travel is possible only at specific, well mapped-out points means that a force of capital ships is unlikely to get the jump on a carrier, but also means that any jump point into enemy territory can be mined and fortified (though they rarely ever seem to be). Jumppoint FTL travel also allows for the “Get on or get left behind” sort of combat landing of small craft aboard carriers seen in BattleStar Galactica, although FTL-capable fighters would be able to cover their motherships until after the jump, at which point they’d simply have to jump out behind the carrier.
The Honor Harrington series of books uses a somewhat arbitrary limitation on the ships (due to the gravity wedges formed by their engines, a ship can neither attack nor be attacked from directly above or below) to make broadside-to-broadside combat the order of the day, with capital ships forming wall formations to maximise their collective firepower. The weapons of choice are thermonuclear missiles, traveling at very high speeds, and powerful beam weapons, used at shorter distances. Smaller missiles and lasers are used to knock down incoming missiles and small craft. In the later books, small, fast gunboats and missile boats are also used in large numbers to swarm enemy capital ships, overwhelming the ships’ defenses by attacking from multiple directions, often in support of friendly capital ships that are carrying out their usual missile broadside attacks. Electronics warfare is used extensively to conceal the position and/or identity of ships and fleets, or to cause incoming missiles to veer off course.
As for how a future space battle would happen in real life? You probably would see, as has been mentioned by others here, capital ships equipped with long range drones and missiles fighting it out at very long range. A ship would likely be lightly armored, unless some revolutionary discovery was made in regards to powerplants or lightweight, effective armor. The last 50 years has shown a dropoff in the use of heavy armor on warships as it is, as it has become more economical and practical to find ways to shoot down incoming ordinance or to destroy the launcher from beyond it’s practical range. You probably won’t see fighters, though you could see various small craft piloted by humans for utility purposes.
You would likely also see drone ships, such as a freighter or a picket ship that requires no human crew, traveling on a pre-programmed course with pre-programmed (or possibly even calculated on-the-fly) responses to situations. A warship would most likely have a human somewhere in the command circuit, even if he was at a desk thousands of kilometers away, his only job to tell the computer “yes or no” on any given course of action.
That said, from a literary standpoint, fleets of droneships fighting it out at long distances just isn’t as entertaining as having squadrons of fighters duking it out in a big furball while their motherships beat eachother senseless at close range, even if it isn’t very realistic.
), that they do have a good way of spotting nukes (“radiological alarm!”) and a fighting chance of intercepting incoming nukes before they enter kill range, then it makes sense to have Battlestars be massive.