I also went with the HD tach, but took it a step further and bought the HD billet tach handlebar clamp, installed high output LED's (2 reds,1 blue, 1yellow) into the clamp, to compliment the L-R turn sig indicators, neutral indicator, and security indicator. It is much, much easier to see the tach and indicators on the handlebar than looking down at the speedo.
Here is the clamp...I had to drill holes for the LED's, this mount was solid.
There are other brands that may have holes for lights already predrilled, but I did not want to gamble with an unknown.
Not the best picture in the world, but the project did turn out great.
Jshuster- I am also in the market for a tach for the nighttrain. I'm looking at the Autometer 2 5/8 inch-Black Dial with a Black cup.Part #19304/$269.00. Cycle performance products sells the tach mount that I like but its also a little pricey. The autometer website has a section for tach's for bikes if your interested. Check them out if you get a minute.