For your first users I think you have to do it "the hard way", by really _selling_ the product. Go manually find the low-hanging fruit for your product. Find the early adopters -- the people who will be delighted to learn your product exists and immediately understand its utility.
Bug all the people you know and get them to use your product where it makes sense.
A couple of good ways 1) create a nifty myspace page explaining the benefit - befriend as many bands as you can and leave them messages
2) Approach some high profile bands to use the product (email is good). Then leaverage their participation to get other bands to use it.
Don't worry about techcrunch traffic - thats the wrong sort of noise you want to make.
My #1 guideline is never pay for publicity. Look for free publicity always!
I also agree that going to shows and introducing yourself to bands will help. Any personal interaction like that would get me to try out the service over a junk spam message on myspace.
There are already quite a few generic mailing list services out there, which is why we're trying to target musicians and build a site centered around fan bases.