Formal:
* До встречи! (Do vstrechi!) - This is the most common and formal way to say goodbye, meaning "Until we meet again."
Informal:
* До скорой встречи! (Do skoroy vstrechi!) - This means "Until soon" or "Until we meet again soon."
* До свидания! (Do svidaniya!) - This means "Goodbye" and can be used in both formal and informal situations.
* Увидимся! (Uvidimsia!) - This is a very informal way to say "See you!" or "Till we meet again."
More specific options:
* До новых встреч! (Do novykh vstrech!) - This means "Until our next meeting."
* Счастливо! (Schastlivo!) - This is a more casual way to say "Goodbye" and can be used instead of "till we meet again" in some situations.
The best way to choose the right phrase depends on the situation and your relationship with the person you are talking to.