Russian River is an absolute must hit. Lagunitas does an excellent brewery tour in Petaluma (and they have a beer garden). Moylan's is a great place to eat lunch and sample beer (just south on the freeway of Lagunitas). Bear Republic is also quite awesome. One time I hit RR, Moylans, and Bear Republic in the same day....it was awesome.
Awesome...I am also heading there in the spring with the wife. We both have never been there. I basically talked her into it and she is all excited. She does not know that we are stopping at Russian River for a few pints.
"Kölsch is the only language one can drink" - Anon
"Good people drink good beer" - Hunter S. Thompson
I live here in Sebastopol about 8 miles away, Stumptown is ok. Guerneville is very eclectic, and very country. There's a sign as you leave Stumptown that says "Leave quickly and quietly, the neighbors have guns" and it's probably true. All the mentioned places are great and easily accessible. Your're staying in Guerneville?