You dont give much info if this is a personal letter or a professional one - I would hope that if it is professsional that you would simply close it with
Thank you for your time and consideration and I look forward to hearing from you int he near future. (If looking for a job)
It depends on who you're writing the letter to. If, of course, you are writing a personal letter to a friend, then yes- it is okay to close a letter with "Forever your friend, Penny."
If you are writing a business letter, it's probably best to go with a more professional closing.