Grog, I had a whole post, with links, all ready, and then I lost it. 
So, here is the stream-of-consciousness version. 
Cannot recommend enough the area around Shasta for cycling. The Summit Century is in August, but you could easily get the route sheets and do the rides on your own. Check with locals to make sure about the snows being gone for the time of your visit. ShastaSummitCentury.com (or .net?) You could easily make Shasta City your base, and do the out-and-back climbs yourselves. BEAUTIFUL. Good roads. Low traffic. If you search on it here on TE you can see some pictures I took last year.
In June, you could do Tour de Blast at Mt. St. Helens. There is a website that Googles pretty easily, and Veronica has done that ride. People say it is a great ride. I'm thinking of it myself this year.
Also in June is RATPOD in western Montana. It also Googles easily, and the person I know who has done it said it was wonderful. I have driven that area, and it is fantastically beautiful.
If you come to the Olympic Peninsula of WA, you could do the Olympic Cycling Classic in late May. The weather at that time is a coin toss...with a lot of gray in recent years for this ride, unfortunately. I would also be happy to share with you some of my local rides around here without the organized ride. Again, there are some pics somewhere on TE I've posted from some of my local rides. PM me if you plan to come this way.
All of these rides include great scenery and good climbing.
"The best rides are the ones where you bite off much more than you can chew, and live through it." ~ Doug Bradbury