Respectfully
Respectfully is a sign off that is tinged with deference, so make sure it suits the occasion. For example, if you are writing to your landlord to enumerate a series of failures and abuses and your closing sentence is something along the line of “Unfortunately, if these deficiencies are not soon remedied, my next step may be legal action,” then ending with “Respectfully” is just awkward.
Warm regards
“Warm regards” is one of those sign-offs that you can experiment with involving warmth. While a word like “warmly” assumes too much intimacy for initial correspondence, ending with “Warm Regards” is both professional and kind.
For business
When writing a business-related letter, it's important that you stay professional and to the point. Try not to end letters with "love," if you can.
Once you've written the body of your letter, write a short sentence thanking your correspondent and summing up what you'd like from them. Phrases like "thank you for your consideration" are great for job applications, and "I await your reply" would be better suited for if you need the other person to respond in a timely manner.
From there, you can just put down your signature, but you can also add another good-bye. "Regards, name" or "respectfully, name" are best for your superiors, and "best," and "thanks," are more informal.
Best
Sometimes signing off with "Best" seems flippant and hurried. Best what, anyway? Best what? Best wishes? Best luck with the task ahead? It leaves in a grey area. But, I like ending with "Best" as it is quick and formal.
Thanks again
Some people say 'Thank You' a lot. Are you one of them? If you have already said 'thanks' once and want to say it again, go ahead. Write Thank you again and sign off with your name. Just be careful not to step on your closing sentence, if that also pertains to gratitude. You don't want to botch the finale with an unwieldy "thanks again again", right?
Yours truly
Yours truly is a sign off that does not stand out. So, if your email or letter states something more important then you should consider writing 'Yours Truly.' It signifies that how you sign off is not the part of this conversation that matters.
