I'm not a big powerseller but I can help ya out.
Starturstore is a good place to buy from. I've seen their knives and other things selling on ebay.
You can also try Link hidden: Login to view. You could start out with children clothing or toys. Also accesseries for popular items like ipods or mp 3-4 players.
Try to sell something your interested in and know a little about.
You have to buy in bulk to make good profit.