Where can I find a good source for  standard decks in Magic: The Gathering?
The best idea is to check out a few sites that are dedicated to the game. Most of them have a collections of Pro players that write for the sites, which gives a lot of insight if you are into reading about the game.

Some other sites provide a resource for viewing decks, seeing what decks work, and also seeing the decklists for decks that have done well at big tournaments.

http://magic.tcgplayer.com/

http://starcitygames.com/

http://www.channelfireball.com/

There are plenty more, but check out these three to start.