It depends on what kind of music you're going for:
If you want good music, listen to Xsjadoblayde and "classical music". If you can't get into classical music, watch Disney's Fantasia. It's all about flow, and classical has the best flow.
If you want popular music, hire someone or figure out the formula that pop music has been using (Aka Silentpony's list). Also, go catchy.
You doing bar gigs, wanna get laid, wanna get high, go popular.
You got a message or want to put your essence out there, go classic (not just classical music, just remember emotion and flow), go "good music", and understand that emotional pain follows (because you could be shamed in front of EVERYONE) (f*** those people tho)
Really it depends on who you are and what you want. If we had more info, we could help more. If all you need is a riff that you can't get right, live your life and it will come to you with time. Don't focus on the now, the best inspiration comes in the whatever. Take a shower and think about it when you haven't thought about it in years. That s*** will blow your mind.
Just including this to emphasize:
Xsjadoblayde said:
Alcohol, drugs, suffering, travel, open-minded curiosity, conversing with strangers, and try not to over-think until after finishing if you can help it. Embrace and push the very limits of your emotions and see what occurs
Also listen to all kinds of music you would never think to normally listen to (even and especially instrumental), poetry of all kinds, along with maybe watching live poetry performers if one so desires