I'd recommend visiting
www.2-pop.com and searching their message boards for information regarding consumer cameras. The first thing to think about is what you'll be using your final films for: Web? Broadcast? DVD? VHS? Then, think about who your audience will be: Industry? Consumers? Etc.
Your price range can get you a decent consumer camera that will do the job. Remember that it's your content and story telling that makes the film. Not, what kind of optics you used or what format; however, if you're going to be using these films to pitch networks then you're going to need something with a 3-CCD since that's what they're used to seeing. You can look around eBay for used Sony VX1000s as they'll be the cheapest (and oldest) 3-CCD cameras.
Also, you said you own an iMac. For $100 you can buy Final Cut Pro Express to edit your films. If you do that, then make sure whatever camera you purchase comes with Firewire (IEEE 1344 or IEEE 1394) This will give you seamless integration into FCP.
There are a ton of other features to think about such as gain-up, manual focus/zoom, audio, etc. If you have any other questions, please let me know.
Sorry if you're purchasing this camera for home movies and the like. Simply ignore what I've posted. I figure, you'd be making short films. If you want a home movie camera, you'll be fine with any Sony or Canon in the $500 price range.