CS Tactical is a good place to buy. When I was in the market for a scope I talked to Mike there for days through email even at odds hours at night, and even though I didn't end up buying from him he was really willing to answer all my questions. He just couldn't get the particular model I wanted for a couple months while someone had the only one left for sale in the US at a good price.
EuroOptic LTD is another good place to buy from, and they have a good selection.
SB USA is also excellent, and has really good LEO and MIL pricing. If that applies to you buy direct from them because you will get the scope at cheaper than dealer pricing.
Edit: The top 2 are both SB and USO dealers.