As developers we have a lot of ideas. Mostly around making overly complicated things simpler.
Most of our "simple idea projects" end up being sold after a year or two to someone who can really give them the attention they deserve.
Here a few of the simple ideas we have put together

Despite covering the most content, this is probably the simplest of our side projects. A website where anyone can request, download, and print various printable documents.
We actually use the site and continue to add content. Launched in late 2010 the site is already picking up a healthy amount of traffic
Launch
We hate multiple websites when one will do. No selection, no validation, no going to another site. Just enter a tracking number, currently supporting USPS, FedEx, and UPS.
Launch
Joe originally made this because he was always losing his phone and this would make it cry out from wherever he had lost it.
Now supporting over a thousand users who prefer to text either anonymously or from a full keyboard.

The tech support guys says, what version of IE are you using? Or What OS are you on? Or what's your IP address?
"How the hell do I know?"
IdentifyCaller.com solves this problem for us and our friends and hundreds of other users everyday.
Launch