I'm assuming you're coming down I-5, at least through Portland. The drive on the west side of the Cascades is going to be far, far more interesting than the drive down the east side of the cascades, so I'd recommend hanging west as long as you can, unless there's something explicit you want to see on the east side.
Recommendation #1: the
Experience Music Project in Seattle. It's in the same area (the Seattle Center) as the Space Needle, so you could see that too. I don't think going in the Space Needle is actually that cool, it's fairly expensive for what amounts to a decent view.
Recommendation #2:
Voodoo Doughnuts in Portland. It's easy to get off I-5 and make it work. Portland's unofficial motto is "Keep Portland weird," Voodoo Doughnuts is an excellent microcosm of that. Get the cock & balls donut, they will decorate it however you like (i.e. your name, your ex's name, something obscene, whatever). This is cheap, quick, and easy, you won't lose much time at all, as they're each within a few minutes of I-5.
If strip clubs are your thing, Portland strip clubs are some of the most liberal in the nation: full nude with alcohol. The popular belief is that Portland has more strip clubs per capita than any other city in the country, but I don't know if that's true. There are a lot of them, however.