I saw a 639 that was in like new condition today at Highsmith Guns in Greenfield for $350 or $375. It really looked nice and if I had some $$$ it would be mine. I like the 39 Series a bit better b/c of it's single stack mag and ease of concealment. It had the adjustable sights and wood grips too.
I have a 3953 DAO Stainless/alloy frame, night sights, recommended by another member, and it is one of my favorite pistols, very easy to carry, a little harder to find though.
I just bought this 6906 from a buddy over on the Ruger forum. Matches up well with Marlin Camp 9 carbine. I paid $400 shipped but got some extras and the gun is like new.