Flaxseed is an excellent source of omega-3 fatty acids, fiber (if you get the whole flax) and lignans (a type of fiber that binds with cholesterol, I believe).
I prefer golden flax (Now brand is one brand). I buy the whole flax seed and grind a cup of it at a time in a small blender cup (my Magic Bullet), storing the whole flax in the freezer, and the ground in the fridge.
If you do a search on 'flax'(in the thread title) in OD, you'll find quite a bit of info on it.