Tom Ricks has started a bit of a firestorm with his list of worst American generals.
1. Douglas MacArthur
2. Benedict Arnold
3. Ned Almond
4. Tommy R. Franks
5. William Westmoreland
6. George McClellan
7. Ambrose Burnside
8. Horatio Gates
55 very intelligent comments thus far about the merits of these folks and others. The discussion is incredibly informative.
Some folks suggest Franks should not be included because the invasion went so well, but he was the one who yes-sirred to Rummy's commandments on keeping the size of the force as small as possible. This allowed a great many bad things to happen, and by not thinking and preparing for the post-war phase, he set the conditions for failure.
I second the high (or low) ranking of General Doug. His ego, the need to protect it, and the coterie he facilitated led to poor decisions. The Aussies were not big fans, as their War Memorial testifies to some poor decisions and lousy treatment of an ally. The lack of preparation for the Japanese invasion, especially with the key air assets vulnerable to bombing, is especially damning.
Anyhow, Rick's post is recommended reading for the comments--not something that is a regular occurrence on the web.