The funniest advancement is for the Assassin Vine. I don't remember, but the bigger one had a CR above the one of the Tarrasque, IIRC.
Shin Okada, Jamis
Buck keep a Random Generator page. The Creature Catalog is managed by Scott Greene (look for someone named Grazzt on these boards) and Erica Balsley (codename DnDChick).
As for myself... I completely dissed the "XP for defeating monsters" system, and just assign XP for story award, roleplaying, danger, ideas... But not on a monster-by-monster basis, rather on a general feeling. The XP I give is also influenced by the level I want the PC to reach (or not reach yet), so it's maybe not always "fair".
Otherwise, I think the CR system (as well as the EL system) is an improvment over what existed before. In AD&D 2, you only had flat experience worth for monsters. Sometimes, by the way, they were very discutable -- for example, a red abishai devil was worth about as much as a hive mother beholder. Let me tell you, offing an abishai was easier, less frightening, and less dangerous task than offin a hive mother.