I gotta say that the 'Take Off' bracket by Kelly bikes works well as an alternative to both STI shifters and down tube shifters. It's a bracket that lets you mount a down tube shifter just below the brake lever on the bars. It is a simple and light system that works well for me on my 'cross bike as I'm too cheap to invest in STI. I haven't tried downtube shifters but I can't imagine how they could be better.
http://www.kellybike.com/2nd_xtra_takeoff.html