My top 5 would be in a state of constant flux, but just at the moment... well, jeepers, even at the moment it's tough. Let me break it down into decades perhaps...
1960s: Top running song of the '60s for me would have to be Steppenwolf's
Born To Be Wild... not exactly a running song
per se but try keeping still to it! Those opening bars for me are the epitome of "get going" music.
1970s: Ah, the decade of disco, Bowie and (dare I say it)... Abba. But my fave big hair song from then would be Deep Purple's
Comin' Home, not one of their better known songs, but brilliant, and from their short-lived line up led by the inimitable
Tommy Bolin - to my mind their bestest front man (sorry Purple fans).
1980s: Can't go past A Flock Of Seagull's
I Ran which I can listen to again and again and again... useful long run stuff.
1990s: Soooo many great songs to choose from, but currently I'm revisiting Chumbawumba's
Tubthumping which has so many drinking references that it's the perfect RC running song
2000s: Still love Jimmy Eat World's
The Middle ... energetic, driving, fun stuff. Love it heaps and has got me through some difficult runs.
What fun