I ahve a Pentax K10 camera, and I really love it, is way better constructed than the Canon Xti or the cheap nikons (d40-50, even de d80). Is a heavy camera, but is water sealed, alloy body, no plastic. You should definetly go for the pentax (maybe the K20d, what a great super machine). Ok the camera is heavy but I have shot continously for hours, and I dont have a big hand or arm.
Considering you have lenses already, go for it, you will not regret it. Look the net, the pentax dslr have Superb reviews.