Not entirely sure if that's the proper term, but I play music, usually ripped CD's, through my PA when I have people over. For the most part things are at a even volume, but then there's the ones that's too low or too loud.
 
I hope I'm explaining this right, but anyone know of a program that will correct this? Maybe use an mp3 as a reference or the levels? I'm just using WMP.

I'd suggest getting Ozone 7... killer deals still going on... It can be used outside of Sonar...and you can import all of your songs, like a set list... and levelize their volumes and other things, then redump them to mp3 or whatever.
 
You can get a limiter or compressor/expander for your pa... hardware used these days should be cheap... guitar center...
 
finally, GOOGLE is your friend... I basically typed     mp3 volume normalizer and got a raft of stuff... here's one:    
http://mp3gain.sourceforge.net/

You are very correct, google is indeed your friend. (especially when you know what you're looking for)
 
Seriously though, thank you. I think that may be what I need.

Check out the original Winamp before version 3.  There are sites that have the old plugins for Winamp. You could search for a limiter.

Media monkey has this feature.

http://www.mediamonkey.com/download/

foobar2000 is another solution 
 

MP3Gain is another possible solution. It's not a player, but rather a volume normalizer actually modifies the MP3 files themselves. However, there is no loss of quality because it merely adjusts levels with no decoding/re-encoding.
 

I was going to mention mp3gain but it was already covered in msg# 2.

mp3gain did the trick. Pretty cool little tool!