Google has introduced search suggestion in YouTube similar to what they already have on the main web search engine.
Now when you make a search on YouTube, a list of related search terms and phrases are displayed adjacent to the search results (see screenshot).
The one issue is that these search suggestions can sometimes be weird. For instance, a search for Google on YouTube threw suggestions like ghosts, upskirt, barbie, porn, etc.
On the other hand, suggestions very extremely relevant for searches like Microsoft, CNN and Paris Hilton to name a few.
Related: Yahoo! Live Search