久仰！ i've heard so much about you.
好久不见了！ long time no see.
辛苦了！ you've had a long day.you've 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.