First off, Donkey Kong 64 was NOT the last good DK game. DK64 is possibly one of the most disappointing games I've ever gone through--way, WAY too much collecting. King of Swing was a bit of a yawn fest as well, but DK redeemed himself in Jungle Beat. That game is ludicrously fun. The Donkey Konga games are fun too, but like the Mario Sports titles, I don't really think of them as being part of the core DK series.
But yeah, other than Diddy Kong Racing on DS, there's not much in the Kong's future (right now) that looks too tantalizing. Here's hoping we can someday get Donkey Kong Country 4 on the DS or something.