Uhm... I'm quite proud of 3 Achievements I have.
The first I got was 'Complete Halo 3's Campaign on Legendary', which I did solo so it felt even better when I got it.
The second, is Hal Life 2's Episode 2 Achievement, 'Little Rocket Man'. I didn't find it as hard as some people make it out to be, but the driving missions were a pain!
Finally, the 'Gobble Gobble' Achievement in Grand Theft Auto 4. I was only pleased with that one because it took me so long to get.