You could surf a site like restorationhardware.com or any of the thousands of outlets that appear by Googling cabinet hardware.

Truth be told, Home Depot, Lowes, Menards, good hardware stores have aisles of the stuff from the really good to the really indifferent.

Knowing what style and type of hardware you are looking for would really help.

That said, I've bought a LOT of knobs, hinges and suchlike on eBay because there are some real bargains to be had - knobs that cost $4.99 each at Lowes cost me about $1.50 shipped from eBay. (First Source Hardware and My Home Hardware are the two sellers I've used most recently). I've also been very happy with Horton Brasses, although they're a bit on the pricey. If you're looking for vintage-y style stuff like glass knobs, VanDykes is a great site. One of the best things about their site is that you can search for (two-hole) cabinet pulls by "boring size", which is the measurement from the center of one hole/screw to the center of the other.

Give KE Hardware a try. I have purhcased a number of items from them for various projects around the house and I have only good things to say!

Here is a link that might be useful: KE Hardware

Does one have to change the hinges as well as the knob/pulls?

Like Johnmarie, I've bought on eBay and saved a lot of dough.

Whether or not you need to change your hinges depends on how well your new knobs match your existing hinges. So you'll save a lot of $ and work if you pick something that matches well enough.

I also purchased from ebay and saved tons of money.

I spray painted my hinges to resemble the finish on the knobs, which are antique pewter.

Does one have to change the hinges as well as the knob/pulls?

I just replaced all the cabinet knobs in my house. I had shiny brass and went with ORB. I had to replace my hinges because it looked really bad. I bought the hinges on Ebay. It was much less expensive than Lowe's or Home Depot which is where I was going to get them.

I bought on ebay as well, and couldnt be happier w/my purchases!! The pulls on ebay were $1.24/each versus $3-4 at Home Depot. The hinges were $1.5 for a pair and were $3 at Home Depot. Now, as an added bonus, the cabinets actually close properly!! Guess 20 yrs of grime on the old ones kinda gunked them up and kept them from closing-hee hee.