There are actually quite a few places you can go to. If you check out the top of this page there is a link that says Shopping. If you just hover over it a nice little pop up will give you some other choices as well.
I have shopped at Toolbarn.com and find it to be pretty competitve as far as pricing goes. Sometimes you pay more than at Lowes or Home Depot but many times I find higher quality tools at competive pricing.
I've looked at Rockler and Woodcraft quite and bit and they both have some things that are very nice, especially for a beginner. I am going to look for a beginner's set and start from there. You can't go wrong with a good basic set.
Yes, sometimes you can run into a treasure trove of goodies at an old estate sale or a yard sale. A lot of people don't use the older tools and are eager to get rid of them for various reasons. I got a great hand saw with wonderful hand carved detail on the handle at a yard sale for a great price.
A lot depends on how familiar you are with woodworking tools. If you are new to the tools as well as the craft, I would suggest buying your starter kit new.
I started out with inexpensive tools from HD and Lowes and if I could start all over again, would go ahead and spend the extra $$ on higher-quality stuff from a Woodcraft, Rockler, etc... I would have saved money in the long run. The only thing I do not buy new are hand planes. I get all of them through Craigslist and antique stores.
This is what i have found from my expirence. I would start out with a small arsenal of tools from HD or lowes to get started and get the feel for how things work and also on how to sharpen then cause that in it self is an art. Once i feel more comfortable i would step up to Rockler and woodcraft. After a massive amount of expirence with the tools and most of the hard woods i would leap into the high end brands of lee vally or lie nielson. One of the reasons that you want to start off with a cheap set of tools is because if you are learning on your own and nobody is telling you what to watch out for then you can ruin some expensive sets of tools. I made that mistake a while back ago cause nobody told me that teak soaks up the silica sand from the soil so it dulled all my tools and my blades very quik.
You can get OK stuff from Lowes AS LONG AS IT ISN"T A TOOL THAT CUTS. Any sharp edge type tools (chisels, planes, saws, etc) will be much more useful if you spend the extra $$ and buy quality. Another site that has great hand tools (and a price to show it) is Lee Valley. Take care of those tools and your grandchildren will be able to use them.