I personally started with Disney pins, but got discouraged because that market is about saturated. I still sell some, but not with as much of a profit as I now do with other things.
I've mostly gone with odds and ends around my house, and some pleasant surprises incuded lots of paperback books by the same author. Also, now that we buy and watch DVDs rather than VHS tapes, and my kids are older, I had success with tapes. I sold old aerobics videos in lots of 3, and pairs of VHS movies. The childrens tapes did best.
On a recent trip to WDW, I went to the Belz outlets (Character Premier and Charater Warehouse - yes there are actually 2 separate stores in the same mall complex), and found many items for 50% to 75% off original prices. Since not everybody has the opportunity to shop in Orlando, one can find some success with that.
Finally, go to yard sales. The scope of items that can be found is enormous, and it helps if you try to focus on a theme. Like, right now patriotism & support for our military troops is high, and items that enhance that theme are good sellers. The apron I mentioned above that I bought for a quarter and final bid was $14, was a Hallmark branded "Grill Sargeant" apron that had a military motif on the front. Of course, now that I've describe that, the chances of anybody finding another deal like that are slim. But stay open minded - some things that I have made the most money on are things I didn't like personally and thought were a long shot.
If you haven't read all 100+ pages of this thread, you really should scan through most of it. There are a few earlier posts that had lists of items... you may find that helpful.
HTH - Good luck and have fun!
Oh well - no pain, no gain - right? 
