Oh lovely question! I think all of these options have implied meanings as well as the apparent one and there is a grammar point too!
First of all, I'm not sure it's polite to tell someone you were expecting them when they show up; it maybe implies that you think s/he is late. Just saying "hello" or "glad you could make it" might be smoother.
I was expecting you and I have been expecting you would seem to suggest that the meeting was NOT planned, but that the speaker had an IDEA that the other one would show up for some reason.
Grammar wise, the "I have been expecting you" verb construction suggests that the wait has been going on for longer than in the "I was expecting you" version.
Both imply that the person who arrives probably thinks you were not expecting him. I agree with suzi that have been expecting suggests a longer wait.
The person is apologizing for showing up unexpectedly. You reassure them, "I was expecting you."
The person is surprised that you aren't surprised that they have come. You explain, "I have been expecting you."
Dinner is cold when the person shows up. You say, "I was expecting you at seven o'clock." Depending on context and tone of voice, this could either be a reproach to them for being late, or an apology for not still being ready for them.