One of the best places to start looking for product is to ask the manufacturer(s) of the product(s) you want to sell. This can be a cost-effective approach (eliminating the middle man) when dealing with smaller manufacturers. Also, I've organized a lot of information on this subject in my hub the non-nonsense guide to buying wholesale products for resale, and I hope you find it helpful. I created it in response to questions from fellow ebayers.
Of course, before you buy anything, you need to do research and develop a business plan. When you have an idea of what types of products you want to sell on ebay, you have to look at how those products have done in the past. This includes, for example, searches on ebay for completed auctions, using sites like hammertap.com (click on resources - free) and perhaps paying (maybe just for a few months) for a service like terapeak. You can see other services (both free and fee) in the solutions directory on eBay.
You can also get an idea of what people are looking for by using Google trends.
Best of luck!