You'll need to build it yourself. This is easier than you can imagine! You want a Parallax BS1USB Board.
http://www.parallax.com/Store/Microc...8/Default.aspx
It has 8 input or output ports you can easily program.
You can make it wireless with a EmbeddedBlue Transceiver AppMod
http://www.parallax.com/Store/Microc...%2cProductName
Some one riding up to 300 feet behind you will be able to monitor everything you connect and program into the basic stamp microprocessor.
The simplest setup would be to salvage the sensor and magnet from a defunct wired cycle computer and connect to data ground and one of the 8 ports as an input port. This will send a pulse to the basic stamp input once every revolution of the wheel. Just figure out your tire circumference and figure out how many revolutions it makes per mile or kilometer. Adding cadence just involves another magnet and sensor exactly like the one on the wheel but you program it for RPM. You can add an LCD display if you like and a button or two to control it.