Faith and Welcoming Churches of the UCC -- www.faithfulandwelcoming.org
Monergism -- www.monergism.com
An excellent source for Reformed theology, including free MP3 downloads.
Textweek -- www.textweek.com
If you are interested in studying the lectionary readings for Sunday, this site is for you!
Steve Brown -- www.stevebrownetc.com
A good example of the freedom Christ gives, but be prepared to be inspired. If you think Calvanists can't be funny, then go here.