There are a growing number of vegan cheese alternatives (slices, blocks, dips, sauces, etc) available in grocery stores and online. Every year, tastier and meltier alternatives hit the shelves - give 'em a try if you haven't lately. You can also make your own cheesy sauces/dips pretty easily, usually using nutritional yeast as the cheesy ingredient.
Replace most cheeses with soy/rice cheese alternative products. Our sister site, Veg Products Guide, has a section dedicated to vegan cheese alternatives and a seperate section for vegan parmesan alternatives.
You can also replace cottage cheese or ricotta cheese with crumbled tofu in lasagne and other dishes, but it won't melt or be creamy the way you'd exect it to be (with spices, though, it could be tasty). Note that many vegan cheeses don't melt. For melting cheese, try Vegan Gourmet™ brand of melting cheese alternatives. It tastes great and melts!
