Here are some useful fishing websites that I visit often:
This is site is the best website for looking at current and past flows for most rivers and streams in California.
This site has a lot of information and maps about fly fishing creeks, streams, and lakes in the Sierra Nevada.
Lost Coast Outfitters - Fishing Report
This site is a mash-up style fishing report provided by guides that covers various waters around California. The area of the report is updated randomly but frequently.
Gilligan's Guide Service
This site is a fishing report that follows Matt "Gilligan" Koles and the waters within the Truckee River area in addition to Pyramid Lake. The report is updated frequently.
Kiene's Fly Shop Forums
This site is a forum that a Sacramento fly shop hosts. You can ask questions, discuss, and read about the local NorCal fly fishing scene here.
This site is a mash-up style fishing report that covers several bodies of water in California. The report is updated frequently although the body of water is often random.
Putah Creek Fly Fishing Forum
This forum is a good resource for anglers who are interested in Putah Creek. You can ask questions, discuss, and read about the local Putah Creek fly fishing scene here.
Jon Baiocchi Fly Fishing News
Jon Baiocchi is a veteran guide that specializes in fly fishing Lake Davis, the NF Yuba River, the Yuba River, and many other streams and rivers in Northern California. His blog is a great resource that is archived with over several years of posts regarding his outings and fishing reports.
The Ecological Angler
Michael Carl's site is a great resource for rivers and streams in California. I've bought and used several of the author's publications for the Heritage Trout Challenge.