One antistatic tube of 25 dual D-type flip-flops.
The data sheet is here, though the data sheet is for the similar Fairchild Semiconductor product. Manufactured by National Semiconductor, this 14 pin DIP TTL chip has 2 positive-edge triggered D flip-flops, with true and complemented (inverted) outputs and separate clocks, separate active-low "reset" pins and separate "set" pins. This is extremely high-speed CMOS. The data sheet says it is guaranteed to be fast enough to switch states with a clock frequency of 140 MHz, but what is typical is 160 MHz. But I remember the National Semiconductor data sheet when it used to be up, corresponding to these chips, and it said that it as a minimum of 140 MHz but typical was 200 MHz. At any rate, they are very, very fast for CMOS. If you want to make a high speed frequency counter that works up to 200 MHz and divides the frequency at the beginning to something more manageable, then this chip will likely be the ticket.
For sheer utility for screwing around with digital electronics, this is probably the best chip to buy, even more than nand gates, I'd say. The need for these simply comes up more often than logic gates, and you quite plainly can do more neat things with them using fewer chips than anything else, I'd say, but it of course depends on what you have in mind to do.