It really is up to the game itself as to what's easy or not. It's not really a blanket difficulty thing to me.
Easy ones I've played:
Burnout Paradise (easier than the in-game awards)
Uncharted: Drake's Fortune (same as the in-game trophies, which a lot are "Get X kills with Y weapon)
Super Stardust HD (most of the arcade are easy while the ones for other modes are a little more challenging)
Prince of Persia (Got 2/3rds of them without much extraneous effort)
LittleBigPlanet (Have all but nine and most aren't that hard. The hardest are just 100%/Ace ones and ones based on level creation.)
Mainichi Isshyo (was patched so foreigners couldn't get them a while back, but I've still got my 100%

)
Buzz Quiz TV (most of these are Bronze, Silver, Gold trophies requiring you to win or play X, Y, and Z amounts of each mode)
PixelJunk Eden (most of these are not that hard, but a few will definitely challenge you.)
If you're solely interested in trophy games just for trophies, do not buy:
Pain (a lot of them require DLC purchases and the others are mostly a pain in the ass)
Soldner-X (Hard shmup doesn't make for easy trophies)
Novastrike (like Soldner-X only not that hard)
Warhawk (requires a lot of time and effort to get most of them, though I guess boosting will help a bit)
Resistance 2 (vast majority are single-player-based, which isn't fun enough to play the two or three times to get them all)
Midnight Club LA (A huge timesink for a bunch of these trophies)
Mortal Kombat vs. DC Universe (Most of these are Kombo Challenges, which are a pain in the ass to complete)