While I like to think that I follow prospects pretty closely and know who the "big guys" are, I can't really call myself a prospect expert by any means. Since I don't have the resources to watch prospects on a regular basis, research is the only way that I have to evaluate prospects. There are many sources online that cover prospects but many are very unreliable.
For those owners that compete in leagues with minor leagues, don't sleep on prospects because the hype machine in fantasy baseball is making them increasingly more valuable. Look at how popular guys like Strasburg and Heyward were in last year's drafts. With the return on investment that these young stars provided, imagine what the hype machine will be for a guy like Bryce Harper. In fact, I own the rights to Harper in my dynasty league and I have already turned away some pretty ridiculous offers. As much as I could get for him now, I think it will be twice as much when he gets close his big league debut.
I will go over some 2011 rookie rankings here in a couple of weeks. In the mean time, I will provide some sites that I reference for prospect analysis.
Baseball America-is probably my favorite. They typically release their top 100 prospect rankings around late February and are typically one of the most accurate.
mlb.com also has descent rankings up by position.