Being a college student, money is always short. I'm going to walk you through setting up a high-quality development box with Fedora 18.
***NOTE*** This will be a 2-part tutorial, with the first part about choosing the hardware and the second part about installing Fedora.
Picking your hardware:
Computer hardware is an extremely hard choice to make - doubly so when looking for a machine to run Linux, because nobody offers linux as a default OS option. (Okay, Dell does. Kind of. But I'll cover that later.)
Time to look at specs:
Processor: Anything from an Intel Core 2 Duo to an Intel Core i5 (or if you feel like overkill, go for an i7), you could also go for the ever ambiguous AMD Dual-Core or an AMD Athalon II. I would stay away from the AMD A-Series (for now) though. Although the A series is great for Windows systems, from what I've read there are still issues with Linux systems.
Unless you're doing something crazy or gaming, integrated graphics will do just fine. In fact, it may be preferable because the Intel integrated graphics are well supported for Linux, whilst NVidia is more or less unsupported. In fact, NVidia was called out by Linus Torvalds for being spectacularly bad about open-source drivers. AMD does have open-source drivers available, but I really don't know anything about them.
A decent dev machine should have at least 4GiB of RAM, but feel free to go with anything up to 8GiB. I also suggest getting DDR3 (which is the current standard - chances are that anything you choose will be DDR3).
From there, hard drive space, screen size and cd/dvd drive is up to you. In terms of the original OS, I suggest staying away from Windows 8. Windows 8 introduced something called Secure Boot, which is akin to a locked bootloader and makes it harder to install Linux.
For reference: My Current Linux Machine (Currently runs Arch)
My current machine tackles anything I need to do without thinking about it, although it is a bit old.
In terms of brand, it's really up to you. I tend to avoid Dell because I've had nothing but bad experiences with their hardware. I favor HP and Lenovo.
The cheapest option ($270): The HP 6910p
My suggestion ($501): The Lenovo ThinkPad Edge
The over-the-top option: The Samsung NP700Z7
These are by no means the only machines you can use (Linux will run on just about everything), so feel free to look around on your own!