How many people?
I presume you're thinking about a standing buffet, or are you intending to do something a bit more formal?

Have a selection of cold platters as suggested:-
Fruit Salad/Platter and Yoghurt - good for kids, and people that are really eating brekkie
Breakfast AntiPasto with Pastries and/or nice, fresh bread.

If you want to do a selection of hot dishes then you can repackage traditional brunch flavours into forms that are easier to reheat and serve en-mass.

Kedgeree - most prep can be done in advance, leaving only reheating and final assembly on the day - yields a large serving for little effort and is a little unusual.
Quiches/Tarts - I'd stay away from doing lots of mini quiches and produce a few 12" quiches - bacon/egg (quiche lorraine) - smoked salmon and fennel - leek & gruyere cheese - all very easy to do in advance, if you blind bake the pastry cases and prepare the fillings the day before then all you need to do is fill them and pour over beaten eggs and cream on the day. If you accompany them with a bowl of mixed salad leaves then they will go a long way.