Clock, any form of logic circuit (basic alarm, auto garden watering, flood alarm) pretty much anything **COULD** be made using 2 or more ICs, although it would be wasteful in a lot of cases.
Can you offer any additional information, for example an inteded purpose. Does it have to be logic or any IC, as there is NOTHING that can be built (that I know of) that can be done by an IC that cannot be done using discrete parts, as an IC is just lots of discreets in a very small space.
Other things you could possibly do - make a uProcessor talk to your pc, mabey to measure temp, then send it to your pc via the serial port. that would give you 2 ICs, one for the uP and one for the RS232 converter (eg MAX232 or similar)
Just thought, what technical knowledge do you have with ICs, how simple do you need it to be?