I agree with you about eVent, a waterproof-breathable fabric made by BHA Technologies. Most readers will know that it's a material that is chemically similar to Gore-Tex (ePTFE, more commonly known as expanded polytetrafluoroethylene, a cousin of Teflon) but made with a different process that results in a fabric with more open pores. Alas, the stuff is having a little problem getting traction in the market. Lowe Alpine unveiled a line of eVent jackets in 2003, then yanked it last year in favor of Gore-Tex. I have an eVent cycling jacket made by Pearl Izumi, and absolutely love it.
But, so far as I can tell, no one is making mittens of the stuff, which is too bad. Your best bet, I think, is going to be something such as Outdoor Research's Glacier Mitts ($79, www.orgear.com). They use a proprietary waterproof-breathable fabric OR calls Ventia, which seems to work pretty well. It comes with a mid-weight liner, and that can be removed and replaced with whatever you wish—anything from silk glove liners to a heaver mitt liner. So it's sort of a mitten for all seasons. Mammut makes a Gore-Tex overmitt called the Covermitt (about $90, www.mammut.ch) but they're exceedingly hard to find in the United States.
I'd also take a look at Marmot's Randonnee Mitts ($100, www.marmot.com), which use a Gore-Tex liner for good waterproofness and breathability. The downside is that they're not a modular mitten like the Glacier Mitts. The Primaloft insulation—which is great stuff—is sewn into the mitten. But for regular use in cold weather, they're great. Glove liners can extend the comfort range down a bit further. The same holds true for Black Diamond's Mercury Mitt ($80, www.bdel.com), which combines Gore-Tex with Schoeller fabrics for a great all-purpose mitt.
Stay strong, Dennis. Don't enter that 12-step program!