I use a BCD396XT to monitor the Illinois Starcom21 (a P-25 system) towers in my area and I have been impressed with how well it performs. While I would recommend a BCD396XT to just about anybody, I realize that everyone has a different taste in electronics. Take a look at the BCD396XT and compare it to the GRE PSR-500 and the RadioShack (excuse me, "The Shack") Pro-106. I compared all three of them for quite awhile until I finally decided to get the BCD396XT and I think it's one of the best purchases that I've ever made. Of course, I was in the market for a portable scanner, which is why I compared the above scanners. If you're looking for a base scanner, you would want to examine scanners such as the Uniden BCD996XT, GRE PSR-600, and the RadioShack Pro-197. Ka3jjz gave you some good advice, ask the other users in the Colorado forum what is working well for them, they could probably tell you what scanner(s) performs well on the various systems out there.
Don't forget to check out the RR Wiki for information on all of the above scanners:
Categoryigital Scanners - The RadioReference Wiki