What about Phidgets for the devices/sensors. Connects to the USB port and allows you to connect all kinds of input and output devices (touch sensors, temp. sensors, light sensors, IR sensors, range sensors, PH sensors, accelerometers, etc) (LCDs, relays, etc). The phidgets are all completely programmable through a wide variety of programming languages, and even have their own native web-based API for things like flash. I even ported the base Phidgets drivers and web driver to OS 2008, so code development would be pretty easy.

The downside is that you can't really hook up too much without needing a USB powered hub to add more than one or two sensors. Of course, alternatively you could connect the phidgets to another device/computer and use the web-based API to access them over wifi... it's all possible, you just have to have some practical reason to want to do it, a bit of money to spend on it, and some time/creative abilities.