The least expensive, and one of the most useful alignment "aid" I've ever used is the good ol' driving range ball. It has a nice big red stripe around the equator that's easy to line up on the target line. Best of all, you can get a whole bucket of them for a couple of buck. This is really handy if you play at a course where there's lots of water.
The second best alignment aid I've used over the years is the very same one guys on TV use; pick your line and pick a spot no more than about 6" in front of your ball, on the intended line. A blade of grass, a discolored spot, there's always something to look at. Keep in mind that once you decide on where you want to hit it, all putts are straight putts. Repeat . . . ALL putts are straight putts. Just start it on your line and trust it. TFlan
