I don't know what is popular, but I do know that Garage Sales seem to be the latest "thing", which is great. Recycling! Our local paper has tons of ads now, and I can assume it has something to do with the economy, unemployment, and going green as well.
Moto - I would think that not too many folks are going to Garage Sales looking for motorcycle gear, maybe I'm wrong. Kind of a small market.
I would think expensive, yet "temporary" items - like baby stuff, car seats, and the like would be popular. Other than that... dunno.
Years ago, I used to go to "Estate Sales" and over a course of about five or six years I accumulated tons of old woodworking tools, stanley planes, chisels, bits, measuring and marking devices, etc. I have a whole wall display in my basement workshop of old wooden and otherwise late 1800's to 1950's era planes for every sort of molding or smoothing task. I never paid more than say $30 bucks for any of them, but the "book" says they are worth ten times that. To who... I don't know. I told my wife to sell them off when I kick the bucket!
By the way, I cleaned up, replaced missing parts, and refinished the ones that needed it - they all actually work, and perform the task they were designed for, but I'm told this "refinishing" diminishes the value. Oh well.
Got off topic there, but anyway, tools are another item I would think people are looking for, especially now. Walnecks - the same outfit that publishes the used and classic bike selling magazine - has "Swap Meets" every month around here, Google 'Walnecks' and search further. I go to at least one every year, and always see second-hand gear and ... stuff. If you have enough bike stuff to sell off, that would be the venue.
Ride safe!
I could use a magnetic tank bag for the Zooki.
