Money Mart

Of the few places I have had to cash a check at on a weekend, this is the best. I've never encountered a long line and they provide a number of services, including payday loans, tax returns and western union transfers. They also have a great rate on pre-paid non-personalised visa cards, which I've found are a safer way to shop on the Internet.

This place is your usual check cashing/loan/wire transfer/money order establishment.
In my 8 years in Seattle I have used this particular business for either cashing a check because my bank was closed, or I had to send or receive money through Western Union for an emergency situation. The employees have always been nice and the location is perfect for me, personally speaking.
They have parking available as well.