There is a classified section at woodnet (http://www.forums.woodnet.net/ubbthreads/ubbthreads.php
). Also craigslist is pretty good outlet for tools. Key thing if you post online is pictures and descriptions. It may be possible to sell all as one lot if say its a woodworking shop with decent tools. If its a mix of automotive, household repair tools and misc hand tools it will be less valuable.
Also the quality of the tools will be a big factor in their resale ability. Brands like black and decker, craftsman, royobi, ridgid, kobalt, harbor freight, chicago electric, and others will have limited resale. Brands like Delta, Powermatic, General, Milwaukee, Makita, grizzly, Porter Cable and maybe dewalt will have higher resale. Age doesn't always matter. A 1950s Delta Unisaw in good to fair condition will all parts will sell for close to its new price for instance. A 5 year old craftsman table saw will be worth almost nothing.
If you have any "Big Iron" things like table saws, jointers, planers, etc. let me know and I can give you a bit more guidance for maximizing your return. Also, if you have old woodworking hand tools like planes, chisels, etc. they can have value even if they are very old.