I picked up a gun like this one today. I have an ~8CFM compressor.
[VIDEO]http://www.amazon.com/Campbell-Hausfeld-DH7900-Gravity-Spray/dp/B0009KN9NG/ref=sr_1_2?ie=UTF8&qid=1369847115&sr=8-2&keywords=campbell+hausfeld+gravity+feed+spray+gu n]Campbell Hausfeld DH7900 HVLP Gravity Feed Spray Gun - Amazon.com[/VIDEO]
Along with a whip and an inline filter for my compressor. I'm not really planning on doing guitars at all, but basic DIY shit, wood finishing and some automotive painting.
I figure this is a decent starter gun to get used to it, and once I'm comfortable with the results I'll pick up a better one for the finish and use this for a primer gun.
Painters - what else should I look at getting in terms of paint supplies/tools?
Filters, filters, filters.
Moisture coming through your gun is always a big concern. I started out using only one filter but still got occasional water through the gun, which obviously mucks up your paintjob but also causes your pattern to become erratic. I have a BIG two stage filter on the compressor end of the gun, a small moisture trap before my hose and then one of these Disposable Inline Moisture Filter right on the bottom of the gun. Made a big difference.
If you're using any sort of automotive type paint, know that they're a colossal pain in the ass to clean out of your gun. A good slop sink in the garage will get a lot of use. You'll have to use specialty paint thinner to clean your gun out between use and if you're making a big mess, you'll be using a lot of thinner and it can get expensive and messy FAST.
Extra filters (sorta like these Spray Gun Filters - Pack Of 3 Universal Spray Gun Filters but whatever fits in your gun) will prevent the tiny, fine little inner parts from getting gummed up too bad. If you do that, all you'll need to do between uses is clean your cup thoroughly, toss your in-gun filter, and then spray some thinner/cleaner through the gun and into some paper towels or whatever, and you'll get pretty good use out of your gun without having to disassemble it and clean it under a magnifying glass every time.
That and obviously a good mask/eyewear should get you started.
If you're looking for what kinda paint or material you're actually planning to shoot, that's a different subject.
EDIT: Also, despite everything I said, you'll inevitably have to disassemble your gun and have to clean it completely (either as maintenance or because something will go wrong and get clogged inside). So keep your directions around because reassembly can be tricky the first few times. Those guns usually come with all the tools you need to put them together/take them apart but apart from that, basic hand tools like pliers will do what you need to do.