I ended up with only 8 that I feel strongly are in my personal top X board games. Again, this is a personal list; I'd definitely come up with a different list for games that I'd recommend to others.
1. Through the Ages: A New Story of Civilization
I've only played this version once and the previous edition 4 times, but this is the game I want to play the most. It combines a lot of the game mechanics that I love---drafting, resource management, worker placement, city building---with a theme that just works. It's a long game (3 to 4 hours), but every action you take matters.
2. Agricola + Farmers of the Moor
This is the game that made Puerto Rico obsolete for me. Has a similar role choosing mechanic like Puerto RIco, but adds a good bit of randomness with occupation and improvement cards. IMO, Farmers of the Moor is a must for me because base Agricola boils down to 5 family members or bust.
3. Factory Fun
Basically a tile-laying, engineering game. My brain just loves trying to figure out how to tweak factory layouts to maximize efficiency. This game totally drives some of my friends crazy though.
4. Galaxy Trucker
Another tile-laying game where you rush to build a spaceship, head out on an adventure, and watch your ship get smashed by asteroids and pirates.
5. Pathfinder Adventure Card Game
D&D distilled into card game form. I have a ton of memories of my playgroup's narrow escapes and improbable deaths.
I've watched my friends play way more Tichu than I've played myself. The more I think about Tichu, the more I'm unsure what to say about it. It's a great game; I should rank it higher...
Great cooperative game. Dead-simple ruleset, but very interesting decisions to make each turn because you can see everyone else's cards but not your own.
8. Power Grid
This is the game you want your Accounting or Finance department to be great at. Literally planning your power plant bids, fuel purchases, and electrical grid connections down to the dollar every turn. You either shuddered or got really excited reading this.