First, I want to say, that my answer speaks to a average check at the end. If you want to pay more there are different and exceptional restaurants to go too. If you want cheap food, well, I don't think that exists anywhere in Fort Collins that is not a little bit scary to eat at. =)
I think that the Rainbow is okay, but sometimes it seems like many of their food comes from a can. Although the Bluebird is not strictly vegetarian, it does provide a wide selection of vegetarian choices that are a grade above that of the Rainbow. Each restaurant is located on the north side of Laurel, between Shields and College Ave. Avogadro's Number is also of similar quality to the Rainbow, which is located on the west side of Mason, just north of Laurel.
Yum-yums is also a very tasty choice for some vegetarian fare. They have some of the best falafels in town, far better than the chain restaurants and stylized "Gyro" restaurants. They should, they are ran by a middle-eastern family! Again, it is not strictly vegetarian cuisine. This restaurant is located on the north side of Elizabeth, slightly west of Shields.
If you enjoy indian or nepalanese cuisine then you can go to Mount Everest Cafe, Star of India, and the Taj Mahal - in that order. I love Mount Everest Cafe; their food always being delicious and never giving you a bloated feeling when you have eaten too much. It is located just south of Drake on the West side of Shields. The Star of India is about the same quality as the Taj Mahal, but, unlike the Taj Mahal they will actually make your food spicy (and I like it SPICY!) on request, which is very hard to find. Again, these places have plenty of options for vegetarians and carnivores, alike. The Taj Mahal is on Oak just barely West of College Ave. in old town and the Star of India is off of south College Ave., on the east side of Harvard, I think.
Next too the Star of India is an ethiopian restaurant, which serves excellent fare, vegetarian food included.
That is not even discussing some of the chinese food places. The best tofu I have ever had in Fort Collins came from the Chili House, without a doubt. I LOVE their tofu and am not particularly fond of it in general, being omnivorous. That is located on south College avenue, near Hobby Lobby off of Troutman. There are many other exceptional Chinese restaurants, but these guys are super vegetarian friendly and tasty to boot!
I will be honest, Fort Collins is very vegetarian friendly and you can find tasty cuisine nearly everywhere you go. My suggestion, stay away from the chain restaurants. Not only are you supporting small businesses, your food quality and dining experience will be markedly improved.
