This will not be a comprehensive answer and is intended to kick-start what might end up as part of a FAQ.
Most pulses (the seeds from legumes) e.g. lentils, are a good protein source and are also versatile meal ingredients.
Nuts have high levels of proteins.
Soy is a seed that can be made into tofu or a cow milk substitute.
Have a look at this site (no affiliation) for a good list with explanations and recipes. http://greatist.com/health/complete-vegetarian-proteins