If you're like me, you don't really know your neighbors. I haven't ever been lucky enough to live in a neighborhood where there is a lot of spirit of community....people seem to keep to themselves and like it that way.
We usually have one or two garage sales in the summer (thanks to 2 kids who outgrow their clothes & shoes like crazy, so we always seem to have things around that we don't need/want anymore).
Last time we had a sale, the neighbor across the street came over and mentioned that he has some things to sell, also, so please let him know ahead of time, the next time we're going to have a sale, and he'll have one, too. I was kind of embarrassed that we hadn't thought to mention it to him on our own.
Anyhow, just a thought...if you're looking for an excuse to go over and talk to a neighbor, you might consider letting them know when you're planning on having a garage sale. You could even make little fliers and pass them out in your neighborhood!