ESPN (Churchill and Law) did a bit of preliminary 2011 MLB draft analysis at who the Pirates may take #1 overall. It's an Insider article, so I won't copy anything, but basically Anthony Rendon's still the favorite though questions of his size, struggles playing for Team USA, and ankle are reasons we may look elsewhere.
Cole and Purke are the two most often mentioned as choices here if we don't take Rendon. Law seems to think that both may have bonus demands that price them out of the #1 choice.
Other options could be
Sonny Gray - Short, RHP, Vandy with great makeup
Bubba Starling - Seems like an uber-athlete. 5-tool CF who can also hit 90's from the mound. Considering football as well.
George Springer - OF Connecticut - College bat with big power and athleticism. They mention if Rendon's price is too much, Springer could be a logical choice.