Hard to beat Pyramyd, their prices are not necessarily the lowest, but they have a 30-day warranty of their own on everything they sell. I'd steer clear of the cheaper Centerpoints, most folks like their 4-16x40 model. The Leapers/UTG scopes are pretty good values, my favorite is the 3-9x32. Everyone also seems to like the 3-9 Bug buster and the 3-12x44swat side focus(30mm tube). If at all possible I would try and find a local store where you can handle and look through them, or maybe find somewhere local where airgunners get together to shoot and ask if you can try out what they're using. If you'r set on Centerpoint, I believe Walmart carries them.
I have a Hawke Varmint 3-12x40 on my Marauder, very nice scope for around $200.
Hope that helps,
John