Yet another fantastic cut of meat from Dickson's Farm Stand, this one is grain fed (notice the thick fat cap - on the grass-fed piece there was not much of one). According to the "Cooks' Thesaurus", the culotte is part of the top cap of the sirloin. 
I just grill this bad boy over blazing hardwood charcoal about 4 minutes a side, and then I eat with a compound butter that includes anchovies, garlic, tarragon, and lemon juice. Then, you slice the meat very thinly, parallel to the skewer. This stuff is also very well priced (usually less than $10 per pound) at the most excellent butcher shop in the Chelsea Market here.
On this European site, the culotte is part of the "rumsteak" which is located at #24 in this diagram:
