I'm currently sorting through all my spare Lego pieces and matching them up to parts of sets I don't yet own. It's a long term on-going thing I'm doing to eventually have built every Lego City set ever produced. By City I also mean the Town theme along with the associated extras that go with an urban area, such as a railway, an airport, a sea port and, at a push, a racetrack. I've never been to bothered with the race cars but in my heyday of collecting I bought them anyway so I would like them again just for nostalgia's sake.
While sorting out the pieces into some sort of order I had to take a snapshot of my 'Plate 1x1 round' pieces (below). There are about 420 pieces there consisting of no less than 23 colors, although the picture makes it hard to distinguish white from clear and tan pieces and grays from silver. I have no idea how I came to have so many spare pieces, especially as some of the colors come from sets I don't own and never have!
The average Bricklink price per piece is about 3 pence (UK), or 4 cents (US) so I have around 12.60 GBP (US$ 16.50ish).
I've managed to place most of them in inventories of sets I don't own. The rest, along with loads of other parts I don't have a need for, I'm seriously thinking of opening a Bricklink store to sell them on, or possibly a big pile of bits on eBay which seem to fetch good prices. If I decide either way I'll post links on my blog to them.