I found an effective way to return favors is to pay people in beer (for those who like beer, obviously). Beer is a great equalizer. Get sucked into helping your friend’s fiancee move out of her dorm? Beer. Job taking longer than expected? Beer.
Ooops sorry I broke your [thing you like]? Beer. 
Yes, beer is a wonderful currency. It’s also a nice way to measure time. How long until we leave? Oh about 1/3 of a beer. The only thing is that beer isn’t a concrete measurement of time. My beer may not equal your beer and sometimes my beer is faster than other times. It’s fluid.
I have two beers on tap at the house. I have no problem getting friends to help with various things.
Mind you, it also doesn’t hurt to have a pool table and a hot tub.
In Australia a slab is accepted currency, a slab is 24 cans of beer. I have used beer and in some cases good wine as payment for favors when people won’t take money for petrol etc. Helped a mate move last week and he asked me what I wanted, “slab should do thanks mate”.
In the words of that great philosophizer Homer Simpson “beer is nothing you can’t do?”
I’ve got a student who works in a bike shop, and I bought a nice bike from him. He said “Stop in anytime-- I’ll tune it up, or just clean it up while we jaw.” He won’t take money (even when I catch him nonchalantly replacing cables while we’re chatting!), so I usually show up with a Six Pack of Random Microbrews in my pannier.
It is the perfect “Here’s a little something … that happens to be awesome.” Come to think of it, the Cost-to-Awesome ratio might be the smallest in the world.