During my second year of college I came into fairly close contact with the Z-80 microprocessor (programming it in assembly using a Northstar Horizon), the 741 op-amp (tinkering with a Radio Shack kit for an audio reverb effects machine), and many members of the 74LS series of TTL logic (in a computer architecture class, with lots of labs, involving wiring together gates to make a CPU). I can't quite remember which of those was first, but they were all nearly simultaneous for me. The 555 was in there somewhere, too.