4. Brian Urlacher, MLB, Chicago: As dominant as the Bears' defense has been over the past two seasons, there is no way it would be as threatening without Urlacher in the middle. The Bears lost Pro Bowl defensive tackle Tommie Harris and Pro Bowl safety Mike Brown last season, and Urlacher compensated for those losses with his smarts and athleticism. Just think about what the Bears ask Urlacher to do in their defense. He has to run with tight ends down the middle of the field on passing downs and still be able to attack the line of scrimmage on running plays. How many 6-foot-4, 260-pound linebackers can do that? It says here that the Bears don't want to learn the answer to that.