Well said, Winmag. Any brand names/models you'd recommend?
Eotech and Aimpoint are used a lot by the military. They're pricey, but must have something going for them. Other than that, any good name brand, with the understanding that you'll be paying $100+ for one. Beware of $19 Russian red-dot sights.
Most red-dot sights are 1x scopes with a half-silvered mirror in place of the standard reticle. This is where the dot is projected. The sights are short, because no magnification is required. But the fatter the tube, the bigger the viewing angle. Also, these sights have very long eye relief, so forward mounting is practical.
The Eotech (and a few Russian rifoffs) has no optical tube. It just has a square piece of glass (with metal rollcage) sticking up from the sight body. A hologram of a reticle is projected onto it, and from there, into your eye. It's more expensive, but has the advantage of an extremely wide angle of view. It also has a long eye relief.
Your best starting point is your local well-equipped gun shop, or online at Cabella's or Brownell's.