brandvocates.com - brand + advocates = brandvocates :) great for a social media agency, again didn't get past idea stage
productapi.com - self-explanatory, was going to be somewhat of a amazon-style API of products, but with a "ship" function, grabbed this when I was working with drop-shippers and thought that there had to be a better way
affiliateapi.com - wanted to make a skimlinks-style platform, ended up (recently) with a open-sourced JS-library for GoDaddy affiliate links
giftify.com - send a virtual gift through FB, and the real one arrives at the recipient's door (launched shortly after the FB platform became available, shipped approx 20 orders)
dealreel.com - curate your own list of daily deals from Groupon, etc. and publish it for your friends and followers, wanted to address the fact most deals are crap and there are a select few power users that do look at every deal, wanted to put them to work to find worthwhile deals for the masses, Yipit is doing something cool w.r.t this idea based on normalized sales data: http://blog.yipit.com/2011/08/05/introducing-trending-daily-...
dnsrecipes.com - central wiki w/API listing all the cloud services out there and the DNS settings required to make them work, essentially helping non-techies tie their Google Apps, Tumblr, UServoice, etc. services to their domain in a consistent and visual way, still want to do this at some point as my buddies bug me all the time to do this shit work
logocaster.com - auto-generates an infinite canvas of logo variations (much like the entries page on 99designs) and let's a user refine their logo design based on parameters like color, font-face, emotion, etc.
autowatermark.com - automatically watermark images uploaded to social networks, sadly this is not possible via FB's API or others :(
I'm probably as guilty as any fellow HN'ers of being trigger happy on domain registration when struck by a moment of inspiration. I am happy to see some of the great & fun domains & ideas popping up in this post.