There are some lovely indian "bites" you could try - Onion Bhajis - easy peasy to make the night before and eaten cold on the day (with Raita) for example, or chicken tikka pieces, bombay potato
Or look at Chinese cookbooks/online for Dim Sum and chinese snacks - spring rolls, ribs, wontons, all can be served cold with dips
Or here's a new idea that i plan to use when i next have a get-together, try Tapas cooking - again they are usually easy peasy to make, can be cooked in advance, and served hot or cold - Chorizo in Red wine, Paella, prawns in chilli, patatas bravas etc..... you can make pots of it all and people just help themselves (ala Tapas!). Hope all this is food for thought!