I'll break it down how I usually try to break it down for everyone.
The best thing to look at when buying a Mac is how portable you need it to be.
If you need a basic all-in-one, at home computer that really stays at home, then you are going to want to go with the iMac. If you want something that will allow you to pick what kind of display/screen you have, but it still stays at home, then you're going to want to go with the Mac Mini. The more power hungry version of the Mac Mini would be the Mac Pro, and with maximum upgrades can go upwards of $10,000.
If you're looking for the ultimate mobile computer, then you're going to want to go with something like the Macbook Air which comes in 2 screen options, 11'' and 13''. It's slightly customizable and really really light. It you want something a little more powerful, then you can go with the Macbook Pro, which comes in 2 screen sizes 13'' and 15'', it's not that much heavier than the Macbook Air, but you have a lot more options with like the hard drive and processors.