What is a decent digital camera for beginner-intermediate learners?

I'm currently using a Sony Cyber-shot 10.1 mega pixel digital camera.
I've heard that a real photographer can use a disposable camera to get the shot,
but feel like my camera is equivalent to dial-up as opposed to high-speed.
I know what I want to do, but just can't make my camera do it. It's auto everything.

I've used Nikon cameras before with detatchable lens and love it,
though I have no idea how to use it besides playing around with it or asking my friend what to do.

I want a decent camera for a reasonable price ($300-$500) range that I can learn and advance on and be able to use in future photography classes.

What do you suggest would be a camera for me to look into?

Depends on what you are prepared to put up with.
As I read it, your problem with your current camera is that you don't have manual control. So get a camera that offers manual control. At that stage, basically any camera will do, until you know what you need for what you want to do. I'd propose two choices:
a) used DSLR. For your money, you won't get a new DSLR. Advantage: comes per default with full manual control and a decent sized sensor. Disadvantage: bulky
b) used or new high-end compact or bridge. Advantage: small, easy to carry. Disadvantage: smaller sensor, you're stuck with the built-in lens - and you'll have to look around a bit for one with a decent sensor size and full manual control. I'd suggest the Canon Powershot S series for a compact or G series for a bridge. I'm currently using a S95 - does everything I want (and a few things I haven't even tried yet) and is small enough to be carried everywhere, anytime.

If you want even more control over your camera, you're practically limited to Canon powershots and CHDK (or a remote-controllable DSLR and a laptop… ), an alternative firmware that lets you do some things the manufacturers wouldn't want to support.