For me it comes primarily from on-line marketing, a steady stream of referrals and consistently sending out "Just Sold" postcards after EVERY sale. Trulia is actually one of the best online marketing sources because I have people that want to see their home in the "slide show" of listings on my ad that shows up 100% of the time when anyone searches for homes for sale in my community.
Chris the standard as always: Referrals, expireds, FSBO's, and online marketing for me. Although some have had very good success with neighborhood farming, I have not, and prefer to work many locales so I don't want to be stuck to one area. I prefer to do my online farming by e-newsletters and drip campaigns.