ist wohl die üblichste Form. Ansonsten (je nach Förmlichkeit):

Hasta la vista, baby!
I'll be talkin' at ya.
til then
til later
etc.

Hätte ich auch gesagt, war mir nur nicht sicher. Aber wenn dude mit gutem Beispiel vorangeht ;-)

danke für die Antwort - da muss man erstmal drauf kommen, daß man im Brief "spreche dich später" als Schlußfloskel verwenden kann ...

Student... that's precisely where you're going wrong ... an e-mail is NOT a 'Brief' ... it is by nature a much more informal form of communication and a casual Schlußfloskel is part of the Internet style. If you want to be all formal, write a letter with a fountain pen on real paper and send it by snail mail.

Laters!

Yikes! As a professor who receives emails frequently from students along the lines of "Hi (if even a greeting is included), send me my grade asap, later, xyz" I have to disagree that the email is per definition "informal." People apply for jobs over email, correspond with superiors, etc. and though it is of course more informal than a fountain-pen letter, it should still contain different levels of register according to whom you're addressing. If I were a student, I'd never email someone who has any power over me (grade- or otherwise) without including a polite greeting and a "Sincerely," or "Thank you" or something other than "laters."