I will be in and out of Oregon all summer starting in the middle of may. I will be more in the southern region. A good guide book for creeks is a book called soggy sneakers. It is considered by most in oregon to be the "bible" of oregon kayaking. Also, check out www.oregonkayaking.net
A cool site I came accross a little while ago.
The main season is January until Julyish depending on water, but stuff can usually be found throughout the summer. If you get down to the medford area there is an epic wave in the spring when the water is right.