#1 LowDown - http://mcp.r09.railsrumble.com If you are into cucumber (cukes.info), you'll love this app. It enables you to build specs, and share them them with your clients before implementation. Amazing interface, and huge SaaS potential. I would for this pay right now.
#2 Hi, I'm - http://hi.im Cool way to build a landing page for yourself. This is what google profiles should be. Landing page urls look like http://hi.im/jacques
#3 Omnominator - http://omnominator.com Cute & useful site to choose restaurants among groups. This would be huge as a google wave widget, or integrated into an existing communications platform. The site is incredibly useful on its own though.
#4 Thingivore - http://thingivore.com If you've used delicious library on the mac, this is basically the web version of that. Insanely nice ui and interactivity. This app could make a fortune off amazon's affiliate program.
#5 Neighborhood Watch - http://neighborhoodwat.ch A new peer 2 peer way to monitor web site uptime. You install it on your server and everyone checks everyones websites. Tons of additional data and alerts you could with all the additional servers checking up on you.
#6 Techmeets - http://techmeets.com Nice looking alternative to meetup.com - focused on technical meetups. Crowded market, but this is a decent niche and easy its especially easy to monetize developer eyeballs (job boards, dev tools, etc).
#7 Straightlist - http://husohuso.r09.railsrumble.com Allows you to post and browse installation / deployment steps. Every linux blog on the planet could integrate with this site. Some sort of simple website integration widget is needed.
#8 SmackSale - http://smacksale.com Reddit like tool for tech bargains. Lots of sites already like this, but this one is nicely built and could easily compete among the others. Obvious affiliate potential if they can get traffic.
#9 Nybbl - http://nybblme.r09.railsrumble.com A way to publish small bits of knowledge, with micropayments. Any good hacker comes up with tidbits of useful knowledge every week that he runs across. This could be a neat way to try to monetize that knowledge by getting paid subscribers to these tidbits.
#10 Last Percent - http://lastpercent.com Nice and simple tool to check a website. Looks for broken image links, html validation errors, and css errors. Every developer should use something like this.
#11 Table Surfing - http://tablesurfing.com Cool way to meet new people by setting up dinners with strangers. Would be tough to get enough people on the site to make it useful for finding random dinners, but the site's well designed and looks like it would work well just using it amongst friends
Some awesomely ridiculous apps that deserve mention: - lazeroids.com (online massively multiplayer asteroids). Seriously.
- stomachly.com (restaurant ratings based on bowels)
- celebritypassage.com (tribute site to dead celebs)