Outside of Santa Barbara, Ventura, and San Luis Obispo counties in California, this cut of beef is called a sirloin tip. Not many people have heard of tri-tip, so I thought to share it with everyone.
Whatever the name, this cut is the absolute best for grilling up on a barbecue. It is far superior to a brisket, and I like it better than even most cuts of steak.
It does wonderful in a marinade ... be sure to pierce the meat on each side in 3 or 4 places to let the marinade seep in. It's a very tender cut, so you don't need to let it sit in the marinade for long; a half hour should do it, though the longer you marinade the beef the more melt in your mouth the cut becomes.
My own personal marinade (or basting sauce) recipe is as follows:
1 clove of garlic, minced
Ground bay leaves (optional)
Some stores will offer extremely fatty cuts of tri-tip, so it's best to trim 95% of the fat from the meat, leaving a little to flavor the meat. You can also get pre-trimmed cuts, and usually that's fine, though sometimes you'll not have enough fat, and I find this really affects the flavor.
I usually also grill up some fresh corn on the cob, and garlic bread to have with the meat, and have cheese, wine, and crackers beforehand as appetizers. Yummy!