Stealth Synergy from Ultimate Combat allows all players with this teamwork feat to roll a d20,take the highest roll and then add all your modifiers to stealth. In my current campaign I have a group of 6 players that all took Stealth Synergy and on an average get a combined stealth roll in the the DC 40 to 50 Range.
Has anyone come across any errata concerning this feat,I think it is possibly the most powerful feat in any book. through clever application my players hae used it in several scenarios to simply sneak through enemy lines a coup de grace the enemy commanders, as no NPC can beat thier stealth DC with a perception check.