I just found a pair of KRK Rokit 8s (generation 1) on Craigslist for $300 and picked 'em up. I was thinking the other day, that I probably should have invested in them much earlier in my days of recording. But then again, it would have meant not having a decent condenser for vocals, or not having other mics, cables, stands, etc.
I'm pretty much just rehashing what's already been said, but I do agree with the suggestions already stated.
Depending on your computer's specs/situation, you may want to spend some of it on upgrading the processor or RAM.
It's also always a good thing to have a place to back up data, as you never know when something could go wrong and you lose lots of recordings that may be of great value to you down the road. I used to always have backups and was an idiot and for a short period of time, I had my old, OLD recordings only in one place -- my external drive. I dropped it... and lost it all. It's not sad because the recordings were super great, it's sad because they were the first recordings I had ever made.. and that would have been nice to have down the road for nostalgic purposes.
Anyway, in short (after a long post..), it depends on what you think is important for your situation. Just think about the suggestions posted and go from there.