motivator

there's nothing like having a nice tune in my head to motivate me during a long run. sometimes i run with headphones, but since i sweat a lot, i have typically avoided doing this. nevertheless, i have this i-pod shuffle thingy which is nice and lightweight (i remember the olden days, trying to run with a big-ass walkman or a discman) so i've been rocking out more often. i'd like to put together a mix of tracks for other folks, but i need to know how long to make it. so the question is: how long are your typical training runs? also, should i add warm-up/cool-down tracks?