Hi zhenda,
Right now, with the upcoming yuletide season, TOYS would be one of the hottest things to sell on almost any auction site. There is even a Holiday Toy Guide you can use:
Link hidden: Login to view
But here's something you can do to know what possible products will sell on eBay:
1) Check out the popular searches and most popular products on eBay:
Popular searches:
Link hidden: Login to view
Best selling products:
Link hidden: Login to view
eBay pulse:
Link hidden: Login to view
2) Perform completed listings searches for products or brand names to see the conversion rate and average selling price.
To do a completed listings search, simply click the Advanced Search button next to the main eBay search box. Enter your search keywords as usual, and then check the Completed Listings box. Hit search and you'll see historical data for the previous 30 days. Successful items are in green; unsuccessful items are in red.
Hope this helps. Cheers :)