Pony Express provides a great PO box service -- it's much better than a regular PO box because they'll accept mail from FedEx, UPS, and other couriers (the USPS won't if you have a PO Box through them). The prices are reasonable for renting a box too, and it's conviniently located on 24th street near most the rest of Redmond.
The only catch is they do charge a surcharge to process package arrivals from non-USPS sources. This is because they will actually call you up to let you know you need to come pick the package up, so it covers the time they spend doing that.
For shipping products you are MUCH better off going to the post office or an actual shipper. They won't tack on extra surcharges like Pony Express, and you can save a decent amount of money without going very far.