Undiscovered Country's the obvious one.
The DS9 episode Inter Arma Enim Silent Leges (I had to look up the proper Latin title, but had remember the Eglish form).
The wedding from Nemesis, maybe?
The opening scene from Insurrection, defintely.
Babel, TOS; I have a vague feeling TNG did a similar episode, but aren't sure.
The base commander from the Die Hard TNG episode, "Starship Mine" held a reception for the Enterprise crew.
An early DS9 episode has Bashir looking after a group of diplomats, but I don't remember whether or not we see any actual reception or equivilent.
Depending how loosely you want to take it, every episode of DS9 had a scene in Quark's bar! (Similarly Ten Forward in TNG or the mess hall in VOY).
Be interestd to see how/where this develops. What's your deadline?