The Wall Street Journal, in an article this past January, compared innovation incentive prizes to other ways to encourage innovation like grants, R&D labs, and others. It covers a lot of examples of prizes, giving a lot of attention to Innocentive and the X PRIZE Foundation's work.
Enterprise Resilience Management Blog considers what innovation is all about, and evaluted the WSJ article, and the prize approach to innovation, in that context.
A bit later, in February, Gizmag did an article on the advantages of innovation prizes in the context of the Virgin Earth Challenge announcement. It gives some history about prizes, but I don't agree with everything in the article. For one thing, I think it's a bit overly dramatic and perhaps a bit too early to say "The Ansari X Prize fast-forwarded space development by decades". After all, we don't even know yet whether or not the follow-on vehicles will really be developed, or if they will be commercially successful. I also don't think it's true that "The first recorded prize of this type was offered by the British government in 1714, in the form of financial incentives to the inventor who developed a device capable of measuring longitude within a given degree of accuracy". In fact, I think there were earlier prizes offered (unsuccessfully) for the same problem. Overall, though, you'll get an idea of the types of innovation prizes that have been offered over the years from this article.