Also, when you read Sickels's grades, you'll need to know his grading scale to understand what he's saying, and for whatever reason he doesn't have that in any prominent location on the site. Here it is, courtesy of commenter Mike:
Grade A prospects are the elite. They have a good chance of becoming stars or superstars. Almost all Grade A prospects develop into major league regulars, if injuries or other problems don't intervene. Note that is a major "if" in some cases.
Grade B prospects have a good chance to enjoy successful careers. Some will develop into stars, some will not. Most end up spending several years in the majors, at the very least in a marginal role.
Grade C prospects are the most common type. These are guys who have something positive going for them, but who may have a question mark or three, or who are just too far away from the majors to get an accurate feel for. A few Grade C guys, especially at the lower levels, do develop into stars. Many end up as role players or bench guys. Some don't make it at all.
- Here is Sickels's top 20 list from last year, with commentary as of August, just FYI.