Here are some of my favourite stores to buy backpacking gear online. I would love to hear comments from other readers on where they shop and recommendations they have.
I like this place a lot. They are a store in Oregon that carries a lot of ultralight gear. They have a great selection and knowledgable staff. For me based in Seattle, they are on the UPS route, and so shipments arrive really quick.
Another great site, fast shipping. They carry some things that Backcountry Gear doesn't have.
We have a big REI store just a mile away, I don't really order online, but I do shop there for odds and ends. They have an amazing selection of things.
Pro Mountain Sports
Great tiny local store in Seattle. Good selection of ultralight gear. I have never ordered online from them, so can't comment on their shipping speed.