I used to toss them in the trash. Now I keep/add to a pile of them to be used for various future projects.

I dug out a spot under all of my hose bibs and filled in with rocks so it doesn't get muddy.

Collect them in a pile then occasionally post them for free on a "Freecycle" type website... people will drop whatever they're doing and come running for free rocks. :)

If you have a fair quantity and want to dispose of them on your own time schedule, try a local landfill that accepts clean dirt/clay/rocks/cement/bricks, etc.

In East Portland, one such landfill charges a $10 minimum, but a whole pickup load would probably not be much more than $10.

Walls, pathways, mulching...

I've got a gazillion of those rocks too, although I think in my case it's because this property used to be riverbed. I absolutely *love* rock, but these smooth round ones are rather annoying. You can't make walls out of them, because they're too round, and you can't make comfortable paths out of them, because they're too big; and if you try to mulch with them, weeds just grow right through the cracks and when you try to pull them out---avalanche! I've edged all of my beds and pathways with them, and scattered them in amongst my heat-loving herbs, but I still find myself in possession of piles and piles of the rotten things. I'd love to use them for *something*, but I'm completely at a loss as to what else they'd be good for. If anyone has any suggestions, I'd love to hear them.