Do a google for optics (rifelscopes) etc. You'll find some really good info. I'm pretty sure Bushnell's "Rainguard" is a trademark name for the coating they use.
Most manufacturers do coat their lenses. (If you look at the specs on them, they will say whether they are multi coated, partially multi coated, fully multi coated etc.)
Bushnell Elite series of riflescopes are definately a great bang for the buck!!