Some favorites in no particular order: BBQ, the San Juans, road trips, hiking/camping in the mountains, any activity in the snow, live bands, happy hour, new places to eat, using vacation time, waves, football.
I like trying to use creativity to have fun- that means making music, art, movies, writing, whatever. The end product isnt always good but it's usually a good time.
Any travel is good so as long as it doesn't end up in a third world jail. I like big trips, road trips, weekend getaways, you name it. I know almost every cool spot within a days drive of Seattle.
The outdoors in good weather is the best, why else would we live here? I try to take advantage of being so close to mountains, lakes, etc. Somebody who's up for the occasional camping/backpacking if the weather/stars align is a good thing.
I like someone who can debate or at least handle an opinion they don't agree with, I think some of the best talks come when the honesty flows... Know the difference between disagreeing and arguing.
Having your own life/friends is important. You have to take my word for it right now but I'm not jealous or controlling, I know a lot of guys are, so if that's important to you take note.
I think its good to take at least one awesome trip a year, that means I don't want to plan my next Europe trip ten years out. If you got vacation time, lets use it.
Life is too short to let other people define your happiness for you.