I love Entypo http://entypo.com/

http://entypo.com/http://pictos.cc/http://symbolset.com/http://www.picasicons.com/http://www.picons.me/http://geomicons.com/

In that order.

Lately I've been flipping between Geomicons and Entypo. I've also used symbolset a bit and loved it.

http://geomicons.com/http://www.entypo.com/http://symbolset.com/

No designer can be without Pictos, great base for icons if you're working in Photoshop and great as a set. Big fan of Geomicons as well!

I purchased a bunch thanks to the suggestions!

Here are mine (that haven't been mentioned): http://pixicon.jackietrananh.com/http://glyphicons.com/http://adamwhitcroft.com/batch/

Free: http://www.brankic1979.com/icons/http://www.iconsweets2.com/http://dribbble.com/shots/587469

http://www.iconsweets2.com

Meagan Fisher (owltastic) has a great round up: http://owltastic.com/2011/08/simple-interface-design-icons/

+1 for Entypo