Yours sincerely (when you know the name of the person you're writing to)
Yours faithfully (when you don't know the name and have addressed it "Dear Sir/Madam)
Yours truly has definitely gone out of fashion in BrE, as far as I know.
With letters to good friends, there are many choices and they're very personal:
love from (probably not common in a letter between two males)
lots of love (probably not common in a letter between two males)
See you soon
Bye for now
With love letters, again it's very personal but some options are:
With all my love
I hope those help.
Student or Learner