It's good to give a variety of proteins. We're veggie and meals that I make generally contain one or more of the following:
lentils - as well as dhal suggested above, they don't just have to be used in spicy food - they're pretty versatile and can be made into things like a veggie bolognese or put into stews. There's different varieties of lentils. I would use red lentils for a bolognese, puy lentils for a shepherdess pie for example.
Dried soya mince is very cheap and quick to cook.
I'll have soya beans as a side vegetable quite a lot of the time (you can buy them frozen)
Cans of beans such as chickpeas, kidney beans can be put into stews and casseroles. Flagolet beans make a lovely salad with avocado, spring onions, parsley, olive oil and lemon juice.
Cheese - amongst other things - cauliflower cheese, macaroni cheese
Eggs - french and spanish omelettes.
Tofu - good in stirfries (I've seen recipes where it can be blended into soups to add some protein)
Nuts also a great source of protein (I'm not cooking things with nuts in at the moment because DD is only 21 months old and there's history of allergy in my family)
It's also a good idea to provide things like brown rice/brown pasta/brown bread at least some of the time.
In the past I have found the Vegetarian Society very helpful in providing information about nutritional balance. www.vegsoc.org I contacted them when DD was born and they sent me some free fact sheets.
Another vote for Rose Elliott for good vegetarian recipes. My personal favourite is Sarah Brown (the recipe books of hers that I have have got some good nutritional information too).
HTH