I've got plenty, but I'll stick with four:
-->"Send a Mugshot or Smugshot" in Burnout Paradise. The hard part was that I needed a usb camera, which I didn't have. The easy part was that I found a used EyeToy for $2.00 in a Gamestop. Problem solved.
->"OMGWTFBBQ", completing Resistance 2's single-player campaign on Superhuman. After Call of Duty: World at War's Hardcore mode, I found Superhuman incredibly easy. I had a harder time on Normal with my first playthrough...
-->"Freeflow Combo 40", getting a 40+ combo in Batman: AA. I used the "20-man party" at the end before the final showdown against Joker. Easily got a 64 combo on Normal, first try. Did it again in Hard, just to add insult to injury.
-->"The Lombax Triumphant", R&C:ACiT's platinum trophy. I love Ratchet and Clank, but that game was way too short and easy. Even hardcore mode was a joke.