Lots of the sites I come across are certainly well-known. But that doesn't mean everyone has found them. So, as I find nice and/or informative sites, I like to spread the word to my fellow gamesters. There is a link list in the right column titled "Cool MAME Links" that will continue to grow, here are a few of new additions...
Arcade Endings is a subset of the vgmuseum site that shows in pics the endings of many arcade games. Very cool for someone like me who is too shitty of a player to get there myself.
This site - a subset of the giant Basement Arcade site is a digital warehouse of downloadable manuals - thanks very much!
Lastly, my current best place for down and dirty MAME info, CAESAR's Game Search Page