Though unofficial, a fifteen-year-old by the name of Stephen Ou has created what he now calls iTunes Instant. It uses Apple's Search API to integrate the search results from iTunes, while providing them to you in real time as you search. This was modeled after Google's recent unveiling of Google Instant which functions almost identically for finding search results across the web.

iTunes Instant isn't as fast as Google Instant at the moment, but it beats iTunes regular search by a landslide. As Ou states, “Search within iTunes.app is extremely slow and cluster, I’ve never used it. So I use Apple’s Search API instead, and develop[ed] this app in less than three hours that will make your life better."

You can check out iTunes Instant here.