best cheap easy setup for initial development
mechanical_fish: Ubuntu Linux. You can use aptitude or apt-get to install pretty much whatever you want, it will run on whatever hardware you have at the moment, and it's free of charge.If you already have a Mac you could decide to stick with the Mac OS for development instead (I use it; it works fine), though you will almost certainly not be running Mac OS on your server. So you'll have to figure out Linux anyway sooner or later. The Slicehost tutorials make it much easier -- a lot of the grunt work has been figured out and documented.