I've been pescetarian for three or four years now, and have always enjoyed cooking, so over that time I've come to learn quite a bit about cooking as a vegetarian. Beans are a pretty good source of protein and are rather versatile in their types and what you can do with them. Off the top of my head you get falafel, hummus, black bean burritos, chili, and a bunch of random indian dishes (using garbanzos). Basically all of this can be made with either black beans or garbanzos, sauteed onions and garlic, fresh or canned tomatoes and spices. The secret to vegetarian cooking is knowing how to cook the vegetables to the proper doneness and using the appropriates spices and liquids to make the sauces. It's not that tricky though.
Indian cooking uses A LOT of spices, both in quantity and variety, and you don't really need to know too much to make a convincing dish. Cumin powder, coriander seeds, turmeric, curry powder (get the kind w/o salt added), garam marsala (a bunch of mixed spices), ginger, cloves, nutmeg, and saffron are all spices that can make up an indian dish. They all work pretty well together (save for saffron, which is expensive and has a strong but subtle flavor), so you can either make a dish with a bunch of random spices or try and highlight one using others to accent. It's really about experimenting and learning works best. Checking out recipes and building off them is a great way to figure that out. At any rate, if you start out with some sauteed onions and garlic, and maybe toasted coriander seeds you can turn that into a large number of dishes depending on the vegetables you add next. Chick peas, carrots, potatoes, lentils, green beans, peas, cauliflower, eggplant and tomatoes all work well with indian dishes and different combinations create different dishes. If you can find paneer (fried cheese, basically), it is a good source of protein that works well in curry dishes. Once you've started cooking the vegetables you can add tomato sauce and paste or coconut milk or heavy cream to create some sort of sauce for your dish. That in combination with the seasonings will determine whatever your dish ends up being. I suggest just checking out a bunch of random indian dishes and you'll surely see a pattern emerge.
Moving on, quinoa is a great source of protein. It is a complete protein, whereas stuff like beans, vegetables and cheese aren't. Most meats are complete proteins, so when people worry about protein in their diet, it's not specifically because they don't get enough, but because they aren't getting complete proteins. Although I don't think everyone who worries about enough protein is aware of this.
Greater things to worry about are stuff like zinc and iron, two minerals that we almost solely get from red meat sources. You can get iron from beets, not sure about zinc though. So, if you're going vegetarian it is advisable to take a multi-vitamin in order to ensure you are getting all of the proper minerals. Borscht is a crazy easy, crazy good soup/stew made from beets, carrots and potatoes. It is a very cheap, efficient and delicious way to get your iron.
If your roommates eat fish, I highly recommend you eat things like salmon and tuna, as these are great sources of protein and omega-3 fatty acids. If not, then it is probably wise to take a supplement for omega-3 and omega-6 as well. Sometimes you can find a supplement that contains both, although it is more common to find them packaged separate. Omega-3 being far more common and popular than 6, although both are important.
Pastas and italian food are also a great vegetarian choice. Many of the dishes follow the same example of indian cooking, except the predominant spices are instead rosemary, basil, oregano, and bay leaves. Sauces can be made as a tomato, cream or cheese base. With tomato you just use seasonings, paste and water. With cream or cheese, you use melted butter and cream with both. Cream bases often don't need green leaf spices like rosemary, basil or oregano. Just some salt and garlic usually do. Vegetables for italian dishes include eggplant, tomatoes, zucchini, squash, artichoke, and portabella/cremini mushrooms.
Finally, mushrooms, if you dig them, are a great vegetarian food. They have a fair amount of protein and are pretty hearty. The most versatile to cook with are portabellas, cremini, shitake and oyster mushrooms. Morels are amazing, and only available a limited time in the year. Chanterelles also have an excellent flavor, are more common, but almost equally expensive. Thyme is the number one spice to use with mushrooms, oregano also works well. With mushrooms you can cook up some random dish with other vegetables, in much the manner as you would with indian or italian dishes. Serve with wild or brown rice, and/or with a cream sauce. Sherry is a great cooking wine to use when cooking mushrooms.
ANyway, I could ramble forever about vegetarian eating and cooking. Hopefully this gets you thinking about it in a realistic and opportunistic way, as there are many benefits to vegetarian cooking. You can basically just buy a bunch of random vegetables and if you have the right spices, herbs and seasonings on hand, the variety of dishes you can make are endless. Although I really only mentioned indian, italian, and vaguely mushrooms, there are many other varieties of dishes to try. They all follow the same basic principles, however. Mexican, meditteranean, asian, and latin american all have many vegetarian dishes to offer.
http://www.sooogood.org/iraqi_food_recipes/falafel.htmlI usually just make up whatever for recipes, but here is a recipe for the best falafel that I've ever ate. There is an absolutely phenomenal falafel place by my house, and yet this recipe was even better than they could make. The hummus recipe on that site is also off the hook. Make sure you have a food processor and use soaked garbanzo beans if you make it though.