I used to be doing what you were doing (direct to Amazon), but the recent AdWords changes (namely, one ad per domain) has changed my strategy a little.
Despite pressuring from my father, I've stayed away from Cameras, I wasn't able to get them to convert.
I think that the best products to advertise are ones where the person knows the product name and can type it into a search engine. I think its sort of similar to a kid asking for something specific for Christmas (pick a fad item from the last 5 or 10 years) and they know the name, and they tell the parents to where even they can manage to get the item right. If the kid asks for something more general, he or she is more likely to get the wrong thing (an item from the category, but not the specific one s/he's looking for).
I also think that it's worth looking into building your own site for advertising. If you get your own domain, you can get by the one ad per URL restriction, and you can also offer a range of similar products with links to Amazon, pre-qualify people and giving you a better chance to get the direct link bonus (which can be up to 50% more money in your pocket).
While I've been successful at it, it's taken a lot of work and I've still made a lot of mistakes. Cut your losers, ride your winners, and keep learning - it takes some time, but you should eventually get the hang of it.