Yes. That's a clear violation of the FTC guidelines. If you're presenting a review as an independent opinion without disclosing the fact you're making money from it, that's pretty much exactly what the FTC guidelines are designed to tackle.

If you're just providing links without specific endorsement it's probably fine.

Here's an easier read analysis of the FTC guidelines by the Washington Post:

http://www.washingtonpost.com/wp-dyn/content/article/2009/10...