like, PC133 SDRAM? Or are we talking DDR? I don't normally like to e-bay computer components, but you can get PC133 SDRAM on e-bay for dirt cheap. They're practically giving away the 128mb sticks. You have to start paying for the 256 and up.
DDR memory is still newish, so I would just to go www.newegg.com
and buy it new. Just don't buy refurb or used if at all possible.
The reason I recommend ebay on the PC133 though is that the sticks are like $1 a piece plus shipping. You can get a mess of them for like 15 bucks. Some are bound to work.