For goodness sake - don't for one minute think you have to buy "special" cornmeal to make terrific tasty polenta. Ain't so. And don't bother with the premade "tubes" of polenta (I believe the brand is "Frieda") - they're awful.
Just go out & buy whatever cornmeal your supermarket carries & go to it!!
I, quite frankly, just use good old Quaker Oats brand & cook it up - either with water, milk, or stock, depending on what I plan to do with it. I then let it cool, & cut it & heat it according to how I plan to use it.
My favorite personal indulgence? Cut into squares & sauteed with a LOT of butter & served with eggs for breakfast. Another favorite? Again, cut into squares, sauteed in 1/2 & 1/2 butter & extra virgin olive oil & served with a rich winey mixed mushroom sauce on top. I've never been fond of polenta with tomato sauces, but do know that a lot of folks do enjoy it this way as well.