It’s really hard to beat the speed and versatility of a kayak. I routinely paddle a mile or more upstream without too much effort of the Willamette. You can troll for springers on the Willamette or Columbia, fish for Sturgeon in the winter, fish a small lake or river, or take a kayak into the ocean. Although you shouldn’t attempt this on your own at first. I have a Wilderness Systems Tarpon 120 (12 foot) which I picked up used for $350 fully rigged including a fish finder, which was a steal. I can’t access those boats at work but I’m sure all of them would work. To be able to handle the Willamette, Columbia or the Ocean you want a boat that is over 11’. In general the longer the boat the faster it’s going to be on flat water but at the cost of maneuverability. Probably the most popular boat for the area is the Ocean Kayak Prowler series. There is an 11 foot and a 13 foot version. Most people get one of the Trident series (T11 or T13), which offer additional storage and adjustable foot pegs, although I’m not sure I would spend the extra cash on the Trident upgrade if I was buying one new. I love the Tarpon and for me I feel it’s the perfect compromise between speed and maneuverability. Other models you might consider
Ocean Kayak Scrambler 11-this boat is a bit wider and slower than the prowlers, but it should also be more stable. I know some of the guys on the coast really like this boat. Note it does not come with a seat or rod holders so you will need to do a good amount of drilling and cutting.
Ocean Kayak Scrambler 11 Sit-On-Top Kayak at REI.com
Malibu Kayaks-Also a bit wider and slower but really stable
Malibu Kayaks Stealth 12 Sit-On-Top Kayak at REI.com
Ocean Kayak Frenzy- Also a bit wider and slower but really stable
Prowler T11
Ocean Kayak Prowler 11T Angler Sit-On-Top Kayak at REI.com
Prowler T13
Ocean Kayak Prowler 13T Angler Sit-On-Top Kayak at REI.com
Prowler (non-Trident)
OCEAN KAYAK Prowler 13 Fishing Kayak at West Marine
Tarpon 120
Wilderness Systems Tarpon 120 Sit-On-Top Kayak at REI.com
The best resource you will find is here. I'd post a wanted to buy in the classifieds, there are a lot of guys who have extra boats or who are sponsored and get a new boat every year or every other year.
Northwest Kayak Anglers