The Pacific Northwest's largest city and a longtime center of gay activism throws the hugely attended Seattle Gay Pride Parade and Festival in late June (on June 29-30 in 2013) - it drew more than 350,000 people last year. Also during the weekend is the Annual Seattle Pridefest, a free event at Seattle Center that draws more than 100,000 participants. Seattle's Pride celebrations take place after Capital City Pride in Olympia and Spokane Gay Pride in the eastern part of the state, and typically one week after Portland Gay Pride, just down the I-5 in Oregon.
Quite a few Pride-related events take place during the days leading up to the big Pride weekend. Check the Seattle Pride Events page for specifics.
Also on Saturday, June 29, Seattle Capitol Hill Pride Festival is a massive community event that lasts from 11 am till 11 pm and is right in the heart of the city's main GLBT neighborhood. It features food, music and entertainment (from bands to DJs) on three different stages, a block party, a Paint For Pride Artwalk along Broadway, a Doggie Drag Costume Contest, and more than 100 vendors from local businesses and organizations. One other fun event Saturday is the Seattle PrideFest Family Day, held from noon until 5 in Capitol Hill's lovely Cal Anderson Park.
The Official Seattle Pride Parade is held the following day, on Sunday, June 30, and begins at 11 am at the corner of Union Street and 4th Avenue. It lasts until around 1:30 pm and runs north along 4th Avenue to Denny Way. Here's a map of the parade route. Prior to the parade, at 8:30 am, there's a Pride Brunch at the Palace Ballroom.
Sunday's other big event is Seattle PrideFest at the Seattle Center, which takes place from noon until 8 pm in the shadows of the iconic Space Needle and features entertainment this year from Justin Utley, God Des & She, Alsace Carcione, and many more, plus a DJ stage, a Mural Stage, and an Acoustic Stage. Billing itself the "largest free Pride festival in America," this one attracts some pretty huge crowds.
Additionally, numerous Seattle gay bars as well as gay-popular restaurants, hotels, and shops have special events and parties throughout Pride Week. Check local gay papers, such as Seattle Gay Times, the Seattle Lesbian, and OutCity Northwest magazine, for details. Also take a look at the very useful GLBT site produced by the city's official tourism organization, Visit Seattle.