I use Webfaction, but it's not for everyone (and I get no real traffic).

You get the pricing of shared hosting, but you get SSH access to install stuff in. Combined with the GUI for setting up common apps (Django, etc.), it's pretty nice.

heroku, pagodabox, dreamhost, s3, linode and digital ocean. Each host has their own pros and cons. (Dreamhost for example is slow but they manage everything.) I stay away from rackspace due to issues I've had with them but when they've worked they've worked well.

I'm a huge fan of WebFaction

Absolutely definitely WebFaction for small or entry projects.

If you grow larger I'd go with SoftLayer, not the cheapest option but I've found them to be very professional and reliable.