The absolutely TOP impressive dessert is pavlova. It's very easy, and if you bake it overnight you only have to whip cream and pile on fruit on the big day. Delia's is my recipe of course. I use strawberries, a few raspberries and some blueberries and it always looks amazing!
Delia's chocolate truffle torte would be my second choice. You can make it days ahead, which is a big advantage!
Don't even think about making canape-type desserts! It is hugely time-consuming to fiddle with individual desserts, especially if you have a lot of people coming!
Pretty well what the others say - I would do a combination of : big bowl of seasonal berries (raspberries/strawberries/blueberries) served with selection e.g. Pavlova/chocolate torte/lemon drizzle cake etc etc. Plus big bowl of Nigella's Barbados cream