Buy a corn snake ( rat snake, milk snake, king snake, almost any colubrid ). They usually run about $25 in a pet store, or less if you go to a reptile show. Do not buy a ball python. Balls tend to be picky eaters and stress out easily. Let that be one of your next snakes ;)
The max length of a corn snake is about six feet ( it is uncommon to approach that ), are very docile (on the off chance that you are bitten, it will feel like a light pinch), are hearty eaters, and you don't worry about humidity. These criteria make it (them) the perfect snake!
You'll need a 20-25 gal. tank, a ceramic heater, a hide box (cut an access hole in a shoe box) and a uva/uvb light for daytime light.
Run the ceramic heater constantly (try to keep a steady 85F), but cycle the light roughly 12 hours on 12 hours off. Uva/uvb lighting is very important, without it it is hard for your snake to process calcium and will have weak bones.
Hide boxes make your snake feel safe, without it they will stress out and possibly not feed. Feed your snake [thawed] frozen mice or mice you kill yourself, you don't want an epic battle betwixt your snake and a mouse.
Whatever you do, do NOT use a heat rock. These will burn your snakes belly, and in some cases, will kill it from the burns it will cause.
Check out the links below for some really good dealers of Colubrids. They can be so beautiful!