Tone curve - point curve (lower-right icon) - RGB drop down.
No need for the tone curve - just use the Split Toning panel.
There are 4 cross process presets under "lightroom Color Presets" (Develop Module - left side).
Thanks, I see that now...
@johnbeardy: I've tried to use Split Toning, but so far I'm striking out at coming up with anything that makes sense for the type of work I'm doing (portraiture, wedding).
@web-weaver: Those presets are a bit too strong for my purposes. Tried them out last night. I did come up with some of my own based on curves I've used in the past. Still tinkering...