Machete:
There are a number of bikes out now meant to fit both the road & tri- disciplines.
The one that comes to mind right now (solely because it was in last month's Bicycling magazine) is the new Kestrel Talon.
Comes with a full Shimano 105 drivetrain, but the big thing that makes it road/tri ready is the proprietary seatpost which has 2 mounting positions to offer "road" and "tri" seat angles (probably something like 74 and 79 degrees).
Other than that, just slap a pair of aero bars on a road bike and you're good to go.
(I may, incidentally, have a set I'm not using that I could get rid of.
)
Edit: Also, for a good and cheap cross bike check out the Motobecane's sold through BikesDirect. Not the greatest or lightest frames out there, but definitely worth it. Them and maybe a Surly Cross-Check.