[nycacorp]

Having worked in the technology industry for past 10 years; starting at Globat (Web Hosting) now owned by one of the mega Web Hosting consolidators (who also own BlueHost now); on a side note we were first to go Unlimited bandwidth (pure marketing to compete with BlueHost and it became an industry trend), and working for a CDN (NetDNA and MaxCDN) now; selfless promotion, every Website owner should have a Content Delivery Network these days.

I have to go with Amazon EC2 for your one-time testing instances (location availablity to spin up a box in Ireland or Singapore is great). If your doing some more permentant stuff, then I would have to go with Linode or VPS.net which both are unmanaged vps's. I can't recommend Rackspace cloud, good for some things but not this area. If your looking for application hosting then page.ly or WPEngine is the way to go for Wordpress Hosting, for other application hosting it would be OnApp.