I've been playing since 1.4.4 I think, so I haven't actually been around for that many updates, but in the year or so I have been playing, there have been some pretty awesome updates. :D

1. Fireworks in Snapshot 12w49a
Not huge, but really fun play around with. :)

2. Donkeys in Snapshot 13w16a
I know horses were the big thing in that update, but the donkeys added something to make ass jokes about. xD

3. The /setblock Command in Snapshot 13w37a
I love Redstone and technical Minecraft A LOT. Yeah... I'm a really big nerd. I especially like the /setblock command, because it opens up a whole new world for making adventure maps and stuff. Also, this is the main component to my 2x2 no-piston door.

4. Carpet in Snapshot 13w16a
I don't know why I like carpet so much. I just do. Don't judge me. ;)

5. The New Launcher in 1.6
The new launcher is awesome, and also right after 1.6 came out, my average FPS (on an 8 year old Macbook) went from about 10 FPS to about 30 FPS. :D