I'm in the process of adding more to my home gym and have been trying to follow these guidelines:
First make sure that you have a good room set up with a good amount of space. It's also helpful to have a tv or stereo to keep you in there. I've also added good light and painted the walls white so that it's a little brighter and more energetic.
As far as equipment goes, the first buy should probably be an adjustable bench. I'd buy one that you can do bench presses with and various angles. You should also include a leg extension that you can add weight plates to. I then am purchasing a set of adjustable PowerBlock dumbbells which cover many exercises. Also a good Rack (along with bar and weights) - you can slide your bench right under this. Look for one with a pull up bar and dip station attached. You should be able to do most everything with these. Although, you may want to add a curl bar, a preacher curl bench and cable tower.
Sorry that I don't have pics, but this should give you a good idea of what to start with.