Have a look at Filehippo.com update checker first (Score 0, Offtopic)

I'd recommend having a look at filehippo.com. They have a tool in a similar vein, although not restricted to opensource - the File Hippo update checker (http://www.filehippo.com/updatechecker/) - it works pretty well. My only criticism for them is that they identify new video driver packages which don't necessarily apply to your specific hardware, just the vendor.

On a complete tangent - what software submission sites/distribution channels can people recommend (like fileforum/download.com etc) for getting your own freeware/shareware listed? I've got a guitar tutor thingy at http://www.webprofusion.com/scalex that I want to finally get rolling out, it's been sitting around for ages and I've another update in the works.