This evidently happened a couple of weeks ago, but it was news to me. Cat will not be producing EPA-compliant on-highway truck engines in from 2010 onwards. They have signed a deal with Navistar, and are evidently also going to build a Cat truck.
I gathered that part of the reason was that Paccar (Kenworth and Peterbilt) was going to start producting their own engines in 2010.
Cat was #4 in engines, and Navistar was #5 for large (class 8) trucks this year. (I guess the 6.4L does not figure in this total.)
More info here from the Fleet Owner web site:
Caterpillar, Navistar partnership | Fleet Owner news coverage of Caterpillar, Navistar agreement
I think Ford offered a Cat engine as an option in the F750. So I guess it will be Ford (Navistar) and Cummins only in the future.
Sic transit gloria mundi,
Hank Murphy
2008 F-150 XL