In (American) law enforcement circles, the belt in question is commonly (though technically incorrect) called a Sam Browne, or a pistol belt. You'll find that most modern versions have a stiffener inside, to support the gear that it's called upon to carry.

In those same circles, a Garrison Belt is the slightly thinner (1 1/2" - 1 3/4") trouser belt that goes underneath the pistol belt.

They are usually offered with or without the basket weave pattern.

Personally, I think the width of the pistol belt makes it great for casual kilt wear - especially with Utilikilts. If I were going to match it with a tartan, I'd probably want a plain finish, to avoid the "costuming" look that Dave Dove and Davidlpope referred to.