There are some little accouterments that every butch should have in her fashion arsenal, and one of these is... metal collar stays! Woohoo!!
[Several seconds of resounding silence]
Okay, okay--I know they may seem a little mundane, but if you've never used them before, they will rock your world.
Basically, all men's shirt collars that are neither button-down nor especially casual have little slots on the underside (one on each side). These are where your collar stays go. Many shirts come with plastic ones that, unless you are more fastidious with your laundry than I, are likely to end up warped and thin at the bottom of your dryer.
Metal collar stays are worth buying for several reasons. They weight your collar down better than plastic ones, and keep the points of your collar taut and crisp. This is especially important if you launder your shirts yourself and don't always (or ever) iron. If you forget them in the dryer, no problem--they come out perfectly fine and never warp. PLUS, you can keep them in a little glass jar in your bathroom, which is both convenient and attractive:
It's hard to tell from the picture, but I have two different sizes of stainless steel collar stays. (I've also hung onto the plastic ones that are suitably thick and haven't been been through the wash yet. Most of them are pretty cheap, though, and I just toss 'em.) I recommend getting 6-10 stays of two different sizes (anywhere from 2 1/8 in. to 2 3/4 in. is good--I find that I use 2 1/2 inch by far the most, so now I own mostly those). Some eBay sellers offer good quality items for cheaper than most stores. Don't pay more than a dollar per stay, and don't bother with the plastic ones Banana Republic sells--they're way overpriced for what you get.
Lastly, the Sartorial Butch pointed out a while ago that personalized collar stays make a good butch gift. I feel so-so about this, since no one would see the personalization. Although you could always take advantage of their invisibility by writing hilariously inappropriate things on them. After all, who wouldn't want a collar stay that said "MY BOSS SUCKS" or "NICE VULVA?"