I'm a professional web developer capable of building any kind of
website / web service you can imagine.

I'm looking for a good idea for a website / web service I can build
that will make me lots of money. The catch is that I don't want to
invest much capital to get it off the ground.

All the major ideas have been taken for the most part. eBay.com for
instance charges a comission on every transaction through their online
auctions and they're not falling anytime soon. Amazon.com is growing
and has most of the market share for retail and they're staying around
for a while too. The only way to make money off an e-commerce Web site
now of days, from the ground up for a individual with not a lot of
start-up capital, is to offer products that people just can't get
anywhere else. Selling antiques, artwork, or anything unique -- some
of the most successful sites I've heard in this category sell
everything from doggie collars to custom-made russian-cut jewelry.
But, unfortunately there's no "turn-key" get-rich-quick sites out
there that can make anyone money fast. Anyone who says so is probably
trying to sell you something!