I am looking into this as well for a small sump. You can get hang on the tank overflows from CPR:
<a href="http://www.cprusa.com" target="_blank">http://www.cprusa.com</a>
I use their hang on tank skimmer and it works nicely, but I took the back off my tank stand and realized I could easily fit a sump in there if I wanted to. Its only about 2'X 2', so im not sure how large my sump could be, but I might do it. Im not sure if its worth the work though.