As a musician, I've come up with a few pet things that really help out. Some services will just be entertaining, others will make you rich, famous and powerful. That is, unless you prefer to be good. (There was a dig in there -)).
I, myself, have availed myself of some of these things, and not others. You may ask, why am I not rich famous and powerful? I'd love to say it's because I'm good. In truth, it's that I've become a theatrical producer overseas. Yes, that IS the truth. Don't ask me how it happened.
But I digress. These are still resources to make your music get heard, loved and respected. Check them out!
Programs to get your music onto online sales services, radio stations and such. Some are there to sell your music, others to help get you broadcast, reviewed, recognized.
Software programs to help with backing tracks and MIDI files are here. Also, the famous Music Minus One recordings to practice with a full orchestra.
A unique concept, have potentially hundreds of designers bid for your project. A professional graphic design is a must for any musician to succeed, and this is a way to get it for half or less than what you'd pay at a private agency.
From iTunes to Rhapsody, these are legal ways to listen to every recording (almost, it seems) ever made. There are free trials available here, so you can get a lot of music for a short time without paying bupkis ( = anything, a cent).