Used to end with: "Enjoy the day!"
For more formal stuff, it was always "Best Regards,"
Got too many pieces of feedback from non-recipients about being too casual (never any from recipients though) and plugged "Best Regards" into the Outlook signature box and let it ride from then on.
It gets lost in the big paragraph of "If you are not the intended recipient..." junk anyway, I don't figure anyone actually reads it.
Side note to Marc, interesting feature...I typed in a different (what I considered non-inflammatroy or profane) word in place of "junk" and it blanked it out...cool feature. Sorry I tripped it. Nice job keeping the bar high!