Could you expand your question a bit?

By theme, do you mean a topic to focus the site around, or do you mean a website design theme in terms of the coding and layout?

I would suggest the Amazonia theme that one can get with the Clickbump engine. Very well done theme that I have had success with lately.

Another good amazon review theme mentioned by Jan Roos in his course is the GuitarReview theme. I've used it and it can make a nice site.Probably going to get the Clickbump theme and try that out as well. Its talked about a lot. Sounds very positive.

Just find something easy to read and minimilistic for now, spend your time getting the site up and monetising it.

Focus on the pretty stuff later