好久不见了！
Long time no see.

辛苦了！
Youve had a long day.Youve had a long flight.

尊敬的朋友们！
Distinguished/Honorable/Respected friends

阁下(多用于称呼大使)
Your Excellency

我代表北京市政府欢迎各位朋友访问北京。
On behalf of the Beijing Municipal government, I wish to extend our warm welcome to the friends who have come to visit 
Beijing.

对您的大力协助，我谨代表北京市政府表示衷心的感谢。
On behalf of the Beijing Municipal government, i wish to express our heartfelt thanks to you for your gracious assistance.

在北京过得怎么样？
How are you making out in Beijing?

我一定向他转达您的问候和邀请。
Ill surely remember you and your invitation to him.

欢迎美商来北京投资。
American businessmen are welcome to make investment in Beijing.

欢迎多提宝贵意见。
Your valuable advice is most welcome.