The LM324 is cheap and a Radio Shack item, but the output doesn't swing within 1.5 v of positive supply, so the highest output you're going to get out of it is 3.5V. This could be OK is you used the AR voltage to scale things, but sometimes it's a fuss.
I like the newer CMOS rail-to-rail types/
I use the TLV2372 - an 8 pin dip dual, (2374 for a quad) rail-to-rail CMOS type, in my classes - around $1.00
LMC6482 is also a dual, (6484 for a quad) is a higher current unit that handles capacitive loads, if you're trying to drive anything with the op-amp. around $2.50
A lot of choosing an op-amp depends on what parameter you're trying to optimize. I'm not an EE either, though.
Paul Badger