I'm looking to plan a 4-5 day trip at the end of March to get away from the cold and relax. I've just moved to Seattle from the East Coast where there are a ton of options for this sort of excursion, but I'm not familiar with the West Coast. Is Hawaii the best bet, or is there a closer, more affordable option?
Also, where would be the best place to look for package deals (airfare, hotel, etc). for this sort of trip?
There's no simple answer to this because flight prices vary according to time of the year. Flight costs are probably going to be the highest, and while it is not the only indicator, a lower flight price indicates an 'off-season'. If you try Kayak's Explore feature (set your airport to Seattle) then it does indeed seem that cheapest flights in March 2013 would be for Hawaii. However, costs are also likely to be more in Hawaii - so you could also consider a host of Carribbean / Central American countries that may be slightly more expensive as far as flights go but have cheaper hotels. Besides, you didn't really mention a budget, whether you're going with a family, etc - all factors that can vary the price.
From the West Coast, your main options outside the continental U.S. are Hawaii, Mexico, and Central America. Alaska (often codeshared with Delta) and Hawaiian both have nonstop service from Seattle to Honolulu. You can reach the outer islands and most of Mexico and Central America with a single connection in the West.
Prices will vary sharply with the season, however, and not just in the sense that warm weather destinations cost more in winter. For example, your time frame of late March is rather unfortunate. Getting away from the cold to relax is what millions of college students are also doing in March, and as Easter falls on March 31, 2013, many families are as well. You can often fly SEA-HNL mid-week for under $500, but not in that time frame. Aim for the week after President's Day or April to hit the shoulders.
Similarly, you can get to Costa Rica for a bit more than the cost of going to Hawaii— in October, during the rainy season. For breezy January, expect that price to go up 30% or more.
Since the demise of Travelocity Dream Maps, my usual tool for such planning has been the FareCompare.com Getaway Map, which plots out destinations and prices on a map. Google Flights has a similar, more primitive functionality. Bing Travel, like FareCompare, has tools for tracking trends in fares.
As mentioned in a previous answer, Kayak has a deal finder— it does search for packages deals, just select "Vacations" under "Deal Types"— as do Hipmunk, Travelocity, Expedia, and so on.
I know this is an old posting,but I just thought I'd mention California as a warm, quick, and usually comparatively cheap destination. It's not actually tropical, but if you're just looking for some sun, there's plenty to see and do besides Disneyland. ;-) Also if you're looking for a resort-type vacation, there are some nice places in the Southwest where you would probably get more hotel for your money than some other destinations. All that said, personally I love Hawaii! ;-D
By "place" are you looking for what destinations you should look for a vacation in, or for what site to do your search in? My answer is around the destinations you should try looking into.
Puerto Vallarta is a great option-- most of the time you can even find direct flights from Seattle on Alaska Air.
There are also a lot of smaller towns and beaches less than an hour from PVR as well where you may find less touristy options and much more affordable trips: http://www.rivieranayarit.com/
IMO, these smaller towns are a lot more fun for way less money-- your day to day cost on food and activities is lower there as well. You just pay a cabbie at the airport or organize a shuttle ahead of time.
