Do you have more than one 7474? The neatest thing I ever made from small scale logic like that was shift registers (your basic Kit Car blinking LEDs.) You can probably make an oscillator with the NAND gates, and 2 or more 7474s will make a decent number of blinking lights.
You'll appreciate the arduino more that way as well...
this seems to have some of the details: http://www.docstoc.com/docs/13424256/experiment-7/
A set of bounceless pushbuttons and/or switches are handy to have as well, and should be achievable with the NAND gates. Using your three-input NANDs instead of the usual 2-input gates is left as an exercise for the student.