I would say if you are buying in large volume, the electronics tech field is a good market, possibly the best. It's a fast turnover market, but margin may be small (of course dependent on the exact product) It's important to remember that profit doesn't have to come from high margin, it can also come from low margin, high turnover.
Well this is much harder to specify in all honestly, because this is more of a niche market. The biggest issue with dropshipping is competition, both from wholesale sellers, as well as other dropshippers, so the best advice I could give would be to stay well clear of the high turn over market products, exactly like the electronic tech market.
Deal in slower markets where competition is lower and margin has the potential to be better. Chances are you won't set any sales records, but it's the best chance to find a market when dropshipping in my opinion.
Our Market Research Lab is a good tool for this type of analysis.