Everyday American English Expressions - 1.2 Greetings

4. Greeting a person you haven't seen in a long time

I haven't seen you in years!
Long time no see! (informal) (ltns in SMS and IRC)
I haven't seen you in an age!
I haven't seen you in a month of Sundays!
a month of Sundays = a long time

5. Expressing surprise at meeting someone

What a surprise to meet you here!
Imagine meeting you here! (cliché)
Fancy meeting you here. (cliché)
Never thought I'd see you here!
What are you doing in this neck of the woods?
neck of the woods = part of town; location
What are you doing is this part of town?
What are you doing out of the office?
Where've you been hiding yourself?
What have you been up to?
Shouldn't you be in school?
Shouldn't you be at work?
Have you been keeping busy?
You been keeping busy?
Been keeping busy?
Have you been keeping cool?
You been keeping cool?

6. After you have greeted someone

We seem to keep running into each other.
Haven't we met before?
We have to stop meeting like this. (cliché)
Didn't we meet at that party last week?
I'm sorry; I've forgotten your name.
I've been meaning to call you.

(Reference and source: NTC's Dictionary of Everyday American English Expressions)