I've been using Nikon's D50 for architectural subjects, and I'm considering upgrading to the D7000. Can anyone recommend a good compatible first lens for the D7000? To date, I've considered Nikkor's 16-65 mm lens (around $630), or the 18-105 (for around $400), and I'm looking for a good balance of performance and affordability. In the future, I'd like get the D5100 as my No.2/backup camera. Any suggestions for either camera or lens compatibility would be appreciated.