I make a lovely, really easy (cheats) chocolate trifle:
Base - some kind of sponge cake. You can buy a chocolate marble cake, or a chocolate swiss roll - anything like this. Slice it up and put a tight layer on the bottom of your trifle bowl.
Drizzle/soak (according to preference!) with alcohol - sherry, brandy, Tia Maria, Baileys - whatever you have to hand.
Then you need to top with custard.
Buy two cartons of ready made custard. Into one of them melt some milk/plain chocolate (whichever you prefer); into the other, melt some white chocolate.
Pour one custard onto the sponge, and then the next.
You could also mix in some chocolate polka dots.
Whisk up some double cream till slightly thickened, pour over the top.
Get a Cadbury's Flake. Still in the packet bash it with a rolling pin to break it up/crush it, then sprinkle all over the top of the cream.
If you have to, you can put some fruit into it. I would suggest something like tinned black cherries, as these work very well with chocolate.