The method that I adopt when I need to attend a wedding/party is to keep myself in the receivers' place and think, it generally helps. budget is another one that I keep in mind.
Fathers' friends' childrens' wedding would mean something more dignified than what we would take to our freinds', since the gift wud be talked about by the elders too..
so, shud use discretion, I guess.
if it is a new home that they would be making, then the # of things that you can give wud be lots.. any day to day req. like elcetronics in the kitchen, a tasteful painting for the living room or a romantic one.. any of the krishnas' paintings wud make for any of the rooms

.. for the bedroom, a grandfathers clock, an area rug or a small carpet for the living room to add color, an expensive set of cushion covers, a tasteful set of place mats, or a table runner.. a flower vase from kalanjali.. just about any ethinic stuff from so many shops around..
if the bride is moving into her in-laws' then, their room would make more sense but u need to make it less personal i think, since it is NOt your personal friend, nai..
generally some long standing gift makes them remember you/ ur father
for the thoughtfulness that u wud have put in.. good luck. do let us know what you finally gifted.. have fun.