The best rename software I've come across yet is
Ant Renamer which is also both free and open-source (Its always great to read string manipulation programs, for me at least

)
You can get it
here and explore the various options. It has a ton of them like extracting ID3 info to rename MP3s, and so on. So it won't just stop at helping you with the numbers, you can call on it for a lot other purposes!