In mushroom risotto I'd use a bit of fresh black pepper, maybe a bay leaf for richness, and some thyme (fresh if possible), since the nice woody-smoky flavour goes with mushrooms fairly well. Maybe sprinkle some parsley on top just for garnish, or a dollop of fromage frais or creme fraiche; but as various people have said parsley's pretty powerful so take care. Good stock really is everything in a risotto, but I've had plenty of luck with Knorr powdered stock as well as the concentrated bottled stuff you and I used to use.

...oh, and if you can grate the onion finely (I use the Benriner) and fry it slowly, preferably caramelise it a bit, before you start cooking the risotto, that really helps too; adds a lovely sweetish note.