I typicaly like the Crucial and Kingmax brands of PC2100 with the crucial being a slightly better option if you do not mind increasing the voltage, the Kingmax however performs exceptionally well on default voltages but theres not much between them from my experiences.
Those prices seem a quite steep side, but I agree with UnseenMenace. Don't be too cheap when buying RAM, or you may find that that cheap RAM cost you your overclock. (And isn't that what we're all about?)
Hahaha, I got a 512 Meg stick of generic PC2100 for ~$140 and run at 164 FSB with MAX timings at 2.7V!
What are you looking at for $200+? Are you canadian?
Also, if you really wanna overclock why not look into PC2700 or something, that way it won't be out of spec at all even with 166 FSB, it'll be garaunteed to work at that high a speed. And yeah, it'll work on a board that wants PC2100.