No one give you specifics but the following ar ethe best selling categories on Amazon:
Toys, Kids and Baby
Home Garden and Tools
Sports and Outdoors
Industrial and Scientific category is usually very high paying but needs a lot of work in terms of appropriate content suited to those who are looking at buying some equipment.
Categories like Electronics and gadget related, Movies and even Clothing are extremely competitive with large online sites competing for not just the first page but the first few pages on Google.
Best Sellers in each category sell well and so do "Movers and Shakers", "Most Wished For" and "New Releases" with a good number of reviews.