For our latest project at Boomworks, we’re using a Slicehost VPS for hosting, and Pingdom for server monitoring.
Both of these services I recommend highly.

We’re also using Flyspray for issue/bug tracking/todo management, although I’m researching other options – redMine looks pretty cool.

I’m always on the lookout for new/better ways to manage projects, so: what services do you use in your projects?