wow! a thread about me!
don't worry, i won't let it go to my head
same way everyone else finds out about the stuff they listen to. with me on this board it's a little strange cos not all too many u2 fans are into a lot of the stuff i listen to (proof would be the lack of response i get when i start threads here) since i listen to primarily punk, hardcore and oi! music.
basically, a high speed internet connection and a good college radio station. going to shows and sticking it out while all the other bands play (before the headliners take the stage).
you should check the official sites of some of your favorite bands, quite often they've got link pages with friend bands or similar bands they've toured with. just go through the links, there's bound to be someone you never heard of that you like. smaller record labels are like that to some extent, and they usually house some mp3s on their sites.
right now i'm really into this one band sinners & saints. they put out their album a while ago, but it took me literally until yesterday to get the music in some form. i'm having major issues with my local record shop, but that's another story. i found out about them because i was originally a fan of a great boston hardcore band blood for blood, as well as the ducky boys (also from boston). ducky boys frontman and b4b guitarist are brothers, sinners & saints is a thing they did together. so any side-projects or anything like that. they're not always going to be good...but it doesn't hurt to check them out.