Definitely crispy smoked bacon! I put mine on top with sliced tomatoes and sprinkle the lot with grated cheese before oven-baking. The other really great taste to go with it is peppered, smoked mackerel - just peel skin off mackerel fillets (supermarket bought, already cooked) break them into pieces and tuck in and amongst the cauli before adding the cheese sauce. Brill!
I've just started making a cauliflower and macaroni cheese, it's yum. Also often put some peas in the mix too. On one make of this dish, I chucked in some left over cooked broccoli right at the end and it was lovely. Chox.