Bus/Shuttle Service, Seattle
I traveled with the green tortoise bus from San Francisco, they are a great group, fun to travel with and at a good price.
To get from downtown to the space needle muse the monorail (it's cheep and fast). Seattle has a good bus network.
You can take the bus to:
Ballard, Lake Union, Green Lake, Fremont, Seattle Center, West Seattle, South King County, Downtown Seattle, International District, Chinatown, and Waterfront.
The waterducks are the best way to tour in Seattle. It goes to and around the waterfront. Since driving in downtown Seattle is difficult, might as well have someone drive for you!
Going to places outside of the downtown area are easy to get to by bus. They have a very good bus system and it's cheap. The views along the route aren't bad either.