What type of beef to use?

Beef is probably one of the most widely used products in most recipes today, and oddly enough it's one of the easiest to mess up.  Of course most of our fear with regard to overcooking is all the fear put into us by the media.  The fact is you don't have to kill the beef again by cooking it to death, most of your foodborne bacteria is killed at 140 degrees.   Now there are several different grinds which relates to the beef to fat ratio, depending on the dish you need to use the right grind.  For hamburgers I suggest nothing less than an 80/20 but in my opinion 75/25 is better, fat equals flavor as well as juiciness.  Especially if you a grilling most of the fat is going to drip off into the flame anyway, and it will also aid in retaining moisture even if you do over cook it a bit.  Meatloaf is one area you can certainly afford to go as lean as you'd like 90/10 is good, but you aren't going to get a lot of moisture from the meat so you'll need to make it up somewhere else.  One good way is wrapping your meatloaf in bacon which seals in juices and most of the bacon fat runs off, or by incorporating moisture into the meat like adding A1, Worcestershire sauce.
Another overlooked alternative is buffalo, this is much leaner, has an incredible flavor, and is just as usable as beef.