You'd probably really like the D200. It is not very forgiving of rough technique (auto focus is very quick, but very sensitive), but the results are outstanding. The only thing better from Nikon is going to be the D3x, but that'll set you back $4k.
What kind of glass do you have for Nikon? If you have much of an investment, remember that when you consider Canon.
1999 e46 328i Ti Silver / Black[retired]
2007 e90 335xi Jet Black / Black[retired]
2011 e70 X5 35d Vermillion Red / Cinnamon
2011 e92 M3 LeMans / Fox Red extended