Taking a plane to England in a few days, will be about an 8 hour flight, so I may need some distraction for a few hours.
Can someone please suggest a few good Game Boy Advance titles that will keep me entertained and satisfied that my money was well spent?
Thanks! 
RPG:
Golden Sun (The first one, haven’t played the second so I can’t exactly reccomend it)
Mario and Luigi: Supertar Saga
And Final Fantasy I and II if you’re a fan of the series and don’t mind battle after battle of pretty much the same exact monsters. It gets tedious, but is cool for the nostolgia of it.
Not-RPG:
Wario Ware is a definite must have for anybody with a GBA.
I second both Mario and Luigi: Supertar Saga and Wario Ware. Both are extremley awesome games.
I’ll second Golden Sun (both) and third Mario and Luigi. I’ll also add Mario Kart to the list.
I just bought Tetris Worlds for only $15 and man is it addictive. If you like puzzle games you may like this. The problem is that you keep seeing little falling shapes and trying to fit them together after you turn the game off. But it might be good practice for packing as much as you can in your bags.
If you like adventure games, all three of the Castlevania games are great. My fav. is the second one, but all are good (ther eare pretty much identical to Symphony of the Night for the PSOne.)
Wario Ware is the only GBA game you’ll ever need
Actually, I wasn’t too fond of the second Castlevania game, but Circle of the Moon and especially Aria of Sorrow were amazing adventure games, although i understand that the latter went out of print and is very difficult to find unless it shows up on the pre-played shelf.
If you liked the original, Final Fantasy Tactics Advance is good for the first 10 hours or so, until you realize that all these sidequests are pointless and that there’s really no story to be told
Yes, so far this one is in the lead. Personally i’m not a big RPG fan but I heard this one was well done.
I’ve played Wario Ware as well, and this is the perfect travel quick stop game for the GBA, i’m looking for something more in-depth with a story to finish. Still a great game, no doubt.
All the ‘tactics’ games are good, though after playing a few you will fine that the only thing really different to each is the veneer. I myself have played Advance Wars 2, FF Tactics, Fire Emblem, and Onimusha Tactics, and they were all extremely similar. However, I would highly recommend them; great time wasters! 
Castlevania: Aria of Sorrow is outstanding - maybe the best platformer (although it’s also a quasi-RPG) that I’ve played since Super Metroid, way back when.
If fusoya is right and the game is too difficult to find or too expensive, I’d go with the two older GBA Castlevania games, Mario & Luigi or Zelda: Minish Cap.
I like DodgeBall Advance. Yes, it’s dodgeball, but it’s kinda fun (though it is pretty easy).
Advance Wars and Advance Wars 2. Great games regardless, but also perfectly suited to the GBA.
What Incubus said about the tactics games.
Kirby and the Amazing Mirror and Kirby: Nightmare in Dreamland are good little games. They are harder than the original Kirby with more puzzle solving, but its still Kirby and you get to whack people with giant hammers or (my personal favorite) beat them with your bare hands while wearing a kick-ass handband.
The Legend of Zelda: A Link to the Past. Very good game.
I wish Minish cap had the same control sceme as this game.
I really hate the old GB style of picking a item/weapon for each button.
Unfortunately I have played both games all the way through already, but yes Zelda is an amazing title.
Link to the Past came out on the old school Gameboy, right? I remember playing that game. I heartily recommend it. It was the first time I’d gotten so into a game. I would sneak it into Church and play it even. Too bad I was only borrowing it… I remember wanting to get all the hearts or something, but I had to return it to my friend after a couple of weeks. Was it hearts? What was it? Hmmmm.
The Advanced War series rocks. The games have storylines but you can also just pick them up for a quick battle. Perfect for a long flight or road trip.
Namco Museum and Atari Museum are my two “I must own this” games. Pac-Man, Breakout, Asteroids, Galaga, and so on
Then, one Mega Man game. I like Mega Man Zero 2.
Then some old Game Boy games. Tetris. Mario Land. DSes can not play them, but GBAs and GBA SPs can. Rampage World Tour. Pokemon Yellow.
Then something more complex. Advance War or War 2, or FF Tactics Advance will do nicely.
Nobody mentioned Metroid Zero, either! That’s a GREAT game.
Second or third “Golden Sun” and add one that’s typically in my GBA “F-Zero Maximum Velocity” (or its sequel, “F-Zero GP Legend”).