You should find out the colors the groom and groomsmen are wearing. You SHOULD NOT be wearing the same color ties if you can help it. It won't be the end of the world if you do, that is, unless you are dealing with Bridezilla!
I was the best man at a wedding recently, so I had no choice in my attire, but if I did get to choose, this would have been what I would have worn to the wedding:
I wouldn't want to wear the suit pants if
I didn't have to my girlfriend doesn't make me, but the matching pants seem like the best bet anyway. Currently, the suit is $149 (down from $250) and the pants are $99 (down from $130) on bananarepublic.com.
For a shirt, you can go with the standard (read: safe) plain white shirt:
Or something with just a little flair:
Slim fit non-iron lavender (sweet lilac) striped shirt $69 (down from $79):
Two tie choices:
Or the textured solid silk tie ($59):
Socks (brown, argyle $10):
The Asher Penny Loafer:
Belt $39 (down from $49)
So you end up with a clean look, like a crisp $100 bill (though it will clearly cost you more than that!)