I've had my wrx for a few months with no problems other than the fuel smell in the cold weather. I was just driving to a pals house and my CEL popped on. The light is solid and not blinking. I have no clue what could be wrong, no funny sounds coming from the engine bay or anything so it may be sensor issues. Just wanted to see what all of you thought. It is about 500 miles from an oil change but I doubt that's it. The car is completely stock with no mods.

 

There is no way to tell just from what you posted. You have to get the car scanned so the code or codes can be read, and go from there.
Autozone will scan your car for free, if that is not an option for some reason ask in your local forum if someone with a scanner can help you out. Get the exact code(s) in Pxxxx format, then search the forums for info on that code. You'll probably find what you need just by searching, if you don't then you can post the information in the appropriate tech forum.