In addition to what you 'NEED', what you might want (IMO):
For playing around with maximum options:
PIC18F4685 (96K, CAN, 40Mhz, etc.)
PIC18F4550 (32K, USB, 48Mhz, etc.)
Replace the 4 (40 pin type) with a 2 for a 28pin version.
PIC18F1320 (18 pin, still an 18F type, 40Mhz)
PIC16F887 (40 pin 'old school')

For playing around with the small ones:
12F683 (8 pin), 10F222 (6 pin), 16F88 (18 pin), 16F777

But that's just my toolbox. Others obviously have different preferences. I don't think I've got anything else in there. I've given away all of my older stock (16F84A, '877A, 18F452, 18F4620). Nothing wrong with any of those, except the newer ones have more options.