Here’s a few more good ones that haven’t been mentioned yet:
Sarek. Spock’s dad comes to the Enterprise to negotiate with an alien race. I’d see this one before Unification.
Parallels. Worf notices things around him changing, but no one else does.
The Game. The other episode guest starring Ashley Judd (Darmok is the first one). Riker sleeps with an alien chick who gets him hooked on a (kinda stupid looking, really) hologram game.
The First Duty. Wesley is involved in a stunt flying accident while in Starfleet Academy, resulting in the death of one of his fellow Nova Squadron members. Robert Duncan McNeil guest stars as squad leader Nick Locarno. The character was essentially modified and renamed Tom Paris for ST:Voyager, and was again played by McNeil. In fact, when I first saw Voyager I had forgotten the exact details from the TNG episode, and thought it was the same character. When I looked up the episode I was annoyed that they changed stuff.
Lower Decks. Sito Jaxa, a Bajoran who was also involved in the Nova Squadron accident, does a tour on the Enterprise. Picard doesn’t like her, although I wonder why he let her on his ship in the first place. Maybe Riker was banging some alien chick when he did the crew assignments and forgot to mention the name to Picard.
Timescape. Picard and some of the crew are in a shuttlecraft when they notice a bunch of bizarre time distortions - sometimes time speeds up, and sometimes it stops or runs backwards.
Remember Me. People around Dr. Crusher start disappearing as if they never existed.
Thine Own Self. Data is on a preindustrial planet, and he has forgotten who he is. The locals think he’s some sort of mountain creature.
Future Imperfect. Riker wakes up in Sickbay to discover he’s 16 years older than he remembers.
Frame Of Mind. Riker stars in a play about a mental patient in an asylum, then he actually is a mental patient in an asylum. (Interestingly, Buffy The Vampire Slayer did a similar episode - Normal Again - except without the play framing it. The way the Buffy episode ended left it a bit of an open question whether Buffy really was the Slayer or just trapped in a delusion.)
Conundrum. The entire crew suffers from amnesia, and finds themselves at war with a technologically inferior race.
Disaster. Holy shit, Troi takes command of the Enterprise!
Face Of The Enemy. Holy shit, Troi takes command of a freaking Romulan Warbird!
Ya know, I have to ask how one would go about buying single episodes. I’ve only ever seen TNG (and most other shows, for that matter) sold in complete season sets. Hell, you might as well buy them all anyway. Sure, a lot of the early episodes suck, but they lay groundwork for the later ones. TNG doesn’t have as strong of story arcs as more recent shows, but I think it helped start the trend.