Just bought a new bike last week -- spent more money than I ever thought I would on the bike... but I love it. And even though it's a very nice bike (in my opinion) with some nice accessories, it's still thousands of dollars cheaper than any sort of car. Every day I bike to work I save $1 in gasoline, assuming gas prices are around $3/gallon.
Haven't convinced myself to sell one of our current cars yet, I'm pretty sure I'll convince myself before too long. Right now, the thought of biking through the winter <30 degree weather with wind (and possibly icy trails/roads) is what's holding me back... which is pretty pansy of me, because I hail from Minnesota and am now living between DC and Baltimore... Winters out here are much better winters than the Midwest. Apparently, though, bodies adapt to warmth pretty quickly. That means they'll adapt back to cold just as well, right? :)
Anyway, if I do sell a car, that's an extra ~$6k in our pockets right now. Plus ~$750/year in insurance. And no more oil changes (~$80/year), no more car repairs (~$400/year, but this can vary greatly), no more license tags (~$90/year, I believe)... and one less depreciating hunk of steel and rubber laying around. In just annual expenses and gasoline I'd be saving about $4.60 per day by replacing one of our cars with my bicycle. The extra $6k we get for the sale and the thighs of steel I get from riding are just icing on the cake. Man. I need to sell one of our cars. Biking every day this week felt pretty badass, but there's obviously a ton of progress to be made!