I've been constantly consulting LactMed to see what I can and cannot take. This covers a very wide range of brand drugs and generics, and prescription and over-the-counter drugs. There's even an app for iPhone and Android users.
If you're looking to discuss medicines while breastfeeding with someone over the phone, please check out the InfantRisk Center. They're open from Monday through Friday, 8am-5pm Central time. The InfantRisk Center is run under the direction of Dr. Thomas Hale. Yes, the Dr. Hale.
As usual, Kellymom.com has a great list of websites to check for medications to use and avoid during lactation.
Off to get some Mucinex without psuedoephedrine. Here's hoping that I feel a little bit better soon!
*This list is by no means complete. Feel free to leave any resources I may have missed in the comments.