Sauce Labs

In his talk on screen recording APIs, Jason Horn mentioned he's an avid fan of Sauce Labs and their hosted Selenium solutions. There are a host of features and pricing starts from free (Linux and FireFox, limited to 500 min/month) and goes up to monthly and enterprise pricing. You can try some of the premium services with a free trial if you want to check it out. While I haven't personally used the product, I really like the idea and I'll have to check them out on an upcoming project.