Collar pins can be worn with either point or club (rounded, which are difficult to find off-the-rack) collars. They look great; are appropriate with basically any jacket and tie combination, whether it be as causal as a corduroy odd jacket or as dressy as a double-breasted, chalk-striped suit; and are one of the little accessories that will distinguish you from the masses.
The trick is to find real ones that pin through the collar, much like a safety pin.
Chain department stores usually only carry the clip-on variety. These function poorly as they have a tendency to become crooked -- or even completely unattached from one of the collars -- during the course of the day. And they belong, as blogger ADG explained so well, in a style category with clip-on ties and clip-on suspenders: to be avoided at all costs.
The barbell style is also okay, but it's less ideal because it's impossible, unlike with the safety pin style, to choose a spot higher or lower on the collar to accommodate a certain tie's knot; and because they require shirts with pre-sewn eyelets, which limits such a shirt's usefulness because you have no choice but to wear a collar pin every time you wear that shirt.
For the longest time, I wanted a real one, but had no idea where to find one. I'll be forever indebted to Will Boehlke for referring his readers to Dallas company Broderick, which sells a huge variety of safety pin and barbell style collar bars.
I bought a gold-tone one from them I believe for $7, with another $7 for shipping.
At the time, they didn't have a silver-tone one for a similar price, so I found one on eBay for $9, including shipping.
At the time I'm posting this, Broderick now has both silver- and gold-tone pins for $7, and the additional shipping is probably miniscule.
The Andover Shop also has them for around $15, presumably excluding tax and shipping.
The aforementioned clip-on variety in a typical department store is usually around $10, so this is one of those rare times when it costs little or no extra to get a superior version.
As you'll see when you visit Broderick, the prices for pins vary widely, from $7 for plated ones to $171 for 14K gold ones. In my opinion, collar pins are something that you should buy as cheaply as possible, because probably no one who sees it will ever know the difference, and the $150-plus you save will buy a lot of other things. I've worn my two sub-$10 pins considerably, and have had no problem with them.
Incidentally, if you're worried, the holes the pin makes in your collar will usually close with laundering; by the time the damage becomes irreparable, the shirt will be suffering other irreparable damage from years of general wear-and-tear.
So try pinning your collar sometime. Just make sure you use a real one.