This website is one I use whenever I travel:

www.outletbound.com

It lists all the outlets in the US and you can judge for yourself if the outlet has the stores you want to visit and is therefore worthwhile. You can sort by location. We are blessed in the San Francisco Bay Area as having many outlets, some of which have been mentioned here. Personally I used to prefer Gilroy over Vacaville, but over the past couple of years Vacaville has added some of the same stores as Gilroy and now it's a toss of the coin as far as I'm concerned. There is a nice higher end outlet in Napa which I also like (Ellen Tracy and Dana Buchman have outlet stores there).