Note that in UK English if you start with Dear Sir or Dear Madam, you should end with Yours faithfully. But if you use the person’s name, you should end with Yours sincerely. This rule may seem arbitrary, but it is one of the rules of formal letter writing that is widely known in the UK; therefore I recommend you stick to it. However, there is no such strict rule in the US.
Here are some example closing sentences for emails:
I look forward to hearing from you.
I look forward to hearing from you soon.
I look forward to receiving your reply.
I look forward to seeing you.
I look forward to meeting you.
I look forward to speaking to you on this matter.
Please let me know a convenient time for us to meet.
If you need any further information, please do not hesitate to contact me.
I will let you know more details as soon as I have them.
Please feel free to call me any time on my mobile: 0099 999 999 999
任何时候都可以打我手机，我的电话是：0099 999 999 999
I would appreciate your immediate attention to this matter.
As this matter is urgent, I would be grateful for a swift response.