Mixwit.com finds
 

One of the new bbcodes you can use here at TFP is the [ mixwit] bbcode.

Go to mixwit.com and find some interesting mixes, some may be interesting looking, others may have interesting playlists.

What's the legality of these kinds of sites?

i believe since they are only searching or receiving posted links and, they aren't hosting any files the appear for the moment in the clear.

there are many places that you can do searches for mp3s including google.