I had to do a DIY mastering job and I used Har-Bal (a standalone eq tool) for the EQing part. I was very happy with how it worked and how it sounded. It's a standalone tool that lets you analyze the audio spectrum of your file and make changes to balance it out. You can also load up a reference to help you shape the sound. While it has a built in limiter, I only used it for the EQ. The rest was done in Sonar with a compressor and a limiter. I won't claim to be any sort of expert, but the results were amazing to me. The songs clearly sounded better.

Of course, Har-Bal is just a tool and not a miracle product. While it is thought of (and is) a visual tool, you still have to have flat monitors and good ears to decide on the final product. Just because you can match the eq of your song to another song doesn't mean it's going to sound just right. One nice feature is it can play back the file and toggle between a reference and the file you're working on to hear the similarities/differences. Anyway, I think it's worth checking out and it's just under $100.