I have a very small lawn service but want to keep my blades sharp. It gets expensive having a service company do it. I have a small grinder. What's the best way to sharpen them--in particular, is there a product that can somehow hold the blade and thus insure an even balance/sharpness? I

HI,
Here is a link, showing pictures and using a file with a blade balancer:
http://www.rd.com/familyhandyman/articles/200004/sharpen/mower.html

There is also an electric drill sharpener, available from hardware stores. It is a coarse or fine sharpener, and has a hard plastic "guide" attached to it... specifically for sharpening lawn mower blades. I only have one mower, and it does work great for just one. I use the method of turning the mower over slightly to one side (not front to back), taking off the spark plug wire, holding it up with a block, getting to the blade with the electric drill and blade sharpener.
Here is a picture of one, under the heading "Unifit Blade Sharpener":
http://www.nextag.com/blade-sharpener/search-html
Best wishes, and good luck.

For quickness, nothing beats a grinder... cheap and simple way to check for balance, put a nail in a post, hang it by the bolt hole and check to see if its level, the side it goes off towards is the side to take more steel off. Hand filing is all right, but very slow. If you have a table and a couple clamps, you can clamp the blade down while you take the grinder to it... other then that, small engine shops should be able to do it dirt cheap.

What angle setting do you use to sharpen circular saw blades ?

Yes, there is even blade sharpening machines available, but you would have to sharpen your blades for quite some time to break even.