I'm still a student and therefore have copious amounts of spare time to spend on side projects. I've never had a place to collect my oddities and curiosities that manifest themselves in the form of web applications or code. I'll try to get this list up to date and keep it that way. No promises though.
Sparkplugs - ExpressionEngine and MojoMotor Add-ons
My most profitable venture to date has been Sparkplugs; a foundry of plugins and add-ons for popular CMSes. I'm constantly working with these tools when freelancing, so I do write a fair amount of extensions, and the best of these turn themselves into add-ons which I subsequently release or sell.
Get in on the extendable action over at http://getsparkplugs.com