Since we're all users here, I figured we could exchange web addresses of our favorite databases.  Here are the ones I use (thanks to all the people who are helping me add to this list):

http://www.chess.com/explorer/

http://chessok.com/?page_id=352

http://www.365chess.com/opening.php

http://gameknot.com/chess-games-database.pl?h=1&bd=0&fb=0

http://www.shredderchess.com/online-chess/online-databases/opening-database.html

http://www.chessgames.com/perl/explorer

http://www.chessage.com/database/opbrowser.php

http://www.chessebook.com/openings3.php

http://www.masterchessgames.com/Chess-Openings-Explorer.htm

http://www.eudesign.com/chessops/

http://en.wikibooks.org/wiki/Opening_theory_in_chess

http://www.csm.astate.edu/~wpaulsen/chess/chess.htm

These last three do not have # of games or winning percentages listed next to their moves and generally run out earlier than the others, but they explain each move in a lot more detail which I find infinitely more useful in making my decisions (especially when the various databases disagree).

What are some other online databases out there that people have found useful?

Thanks to all the users contributing to this list!!  As requested, here is a quick recap of other links mentioned below (see individual posts for more details):

http://www.chesscenter.com/twic/twic.html

http://www.chesslive.de/

http://chesslab.com/PositionSearch.html

http://www.newinchess.com/NICBase/Default.aspx?PageID=400

http://www.openingmaster.com/

Hey, it looks like I'm an administrator here too.  Cool.  So, YES, it looks like I CAN make this topic sticky.  I love your idea, and I will be more than happy to edit the 1st post to include all subsequent databases that are offered up.

This Week In Chess has pgn downloads available. Check the very bottom of the page. http://www.chesscenter.com/twic/twic.html

http://www.chesslive.de/

http://chesslab.com/PositionSearch.html

http://chessok.com/?page_id=98

http://www.newinchess.com/NICBase/Default.aspx?PageID=400

I don't know if this one is good but I used it until I became a member here.

http://www.chessage.com/database/opbrowser.php

This database apparently contains any and all non-drawn games people care to upload to it:

http://www.365chess.com/opening.php 

They have an ECO calculator here: http://www.masterchessgames.com/index.php?main=ECO-Calculator-Submit-Chess-Games  that you can upload the pgn file of your completed games to find out what the ECO is. I uploaded a few of my games to try it out and to my surprise it put the games I uploaded  in their database.  Seems to me they use that to build their database.  So any crazy games anyone chooses to upload to them are in their database.  Personally, I wouldn't  trust a database that has my games and other regular people's games in it; might as well flip a coin.  LOL.  What exactly is the deal with 365chess.com's database?

.

I read in that FSVL forum that it's considered cheating on chess.com to use this database because it has "eval numbers,"  whatever those  are:

http://chessok.com/?page_id=352

What is up with that?  I see lots of people posting that database in vote chess games; it seems to be real popular.   I have not seen anything official from chess.com that confirms what was said in that forum.  I don't see how members are expected to know that only from some obscure post in the FSV League group.  Is there anything official from chess.com?