There are several common synonyms for the phrase "kind regards" that can be used to close professional emails or letters. One popular option is "best regards," which conveys a similar level of warmth and friendliness. "Warm regards" is another option, suitable for more casual communication or when a personal relationship exists between the sender and recipient. "Sincerely" is an old-fashioned but still widely used option that can work well in more formal contexts. Other variations include "yours truly," "all the best," and "take care." Whatever phrase you choose, make sure it matches the tone and intent of your message.