The Nike+ got an “oooh” out of me when it first came out. But then I remembered that I’m slavishly devoted to my running shoe brand, which isn’t Nike. And then I further remembered that I really don’t need my feet to communicate with my iPod. I already know how far and how fast I run.
OP, iTunes has pre-made playlists you can download, pretty specifically geared to runners, I believe. I don’t use them myself, but maybe it’ll help you.
Also, if you search a song on iTunes it gives you a list of similar songs. An “if you like X you may like Y type of thing.” So toss in songs you like and see what else they offer you.
As for suggestions, off the top of my head I’d say download the Rolling Stones, “Sympathy for the Devil,” which has a good tempo for running, as well as being nicely thought-provoking (helps speed the workout along) and Plies, “Can We Fuck 1 Mo’ Time,” which is about a breakup, and the tender/poignant feelings that can arise at those times.