This post is namely for nebulein . This is a list of the scanlation groups I use the most often.
Baka Manga Updates. This is a standard manga update list. It has many different mangas and a listing of the groups that scanlate them. Also, it sometime has short information blurbs about the manga.
Tokudane's Yaoi-Yuri Scanlation Listing. This is a listing of all sorts of yaoi and yuri groups, there websites, mirc channels and yahoo groups if they have them.
Aarinfantasy Forum You have to join to use this forum but it is a good place to get mangas. In the download sections you can request specific ones or just download what people have already uploaded. I get most of my manga from here.
Some of my favourite groups.
Nakama. They are scaning Sex Pistols, as well as many others. They produce nice quality scans. However, they are a little difficult to get downloads from. If you join their yahoo group, in the database you can find links to most of their manga.
Hochuuami. I like these guys as well and you can download their mangas off bittorrent.
Beautiful Soup Junjyou Romantica, Koi wa Itsumo Arashi no Youni, and Private Prince are my favourites. And they have downloads.
Datenshi-Blue Relatively new. But has some interesting mangas coming out soon I believe.
Desperate-Love They have direct downloads.
DokiDoki Have bittorrents.
Essence of Purity I can't get here anymore because I'm in China, but I'm pretty sure they are one of the top groups.
Fushichou Good, but slow to update and no downloads except for Mirc
MegKF Slow to update, and their website doesn't have much info but still a good group/
Memory For You Good and they have bittorrent
Mochi-Mochi Good and has direct downloads
Neoterica Can't get here anymore (China). But I like their manga choices.
Mirc is used by alot of groups. It takes a bit of work to figure out. If you want to try to I can give a idea of how to use it although I by no means understand it all that well.