I work for a small web app development company and we're all pretty addicted to SC2. We play a game at lunch most days if we've got the time, but we're all still quite bad (Top 8 Bronze). Anyway, we were investigating new frameworks the other day, and decided to put together a little web app for the iPad using CodeIgniter & Sencha Touch. It lets you pick your preferred race, and then selecting any of the offensive units from the game will tell you what are the useful counters, eg Charge Zealots > Marauders if you're playing as Protoss.
It's not really polished, but we thought it was a fun way to test out some new technologies we don't normally work with, and maybe some folks that are new to Starcraft will find it helpful. I'd love to hear what people think. You can access it at http://sc2.lbm.co. Fyi, it only works in Webkit browsers, and is best experienced on an iPad.