Theres a few good sites out there. I'm currently using 2 for Achievements one has a PS3 equivalent that I know of.

Xbox Sites:
http://www.trueachievements.com/
http://www.xbox360achievements.org

PS3 Site:
http://www.ps3trophies.org/

Hopefully these can help you guys out. Remember, feel free to make a new topic here asking for help with certain achievements. I'm sure there are many people here willing to help c: