Workholding while drilling is something I've spent some time thinking about. Generally speaking, there are 2 things you have to think about:
1. Work wants to twist. This is always bad... and worse when the work is a sword.
2. Work wants to climb the helical flutes of the bit, especially when the drill emerges through the bottom of a through hole
I recommend that you look at:
1. Heinrich Safety Drill Vise. Lists for around $270 when not on sale at MSC. I have one of these on my personal drill press and there are 2 of them in my shop. It's a similar design to the Wahlstrom drill press vise described below. Both use a bar that can be bolted to the table with a quick-release bolt (so it can quickly be moved for another hole) to prevent the vise from twisting. You can also just rest the bar against the drill column. You can download the dimensions of the Heinrich and Wahlstrom, and you'll find that they have the same height jaws...the heinrich opens a little bit wider (but how often do you need 12" capacity...). Here's what my Heinrich looks like (the purple arrow shows the mounting block that you bolt to your drill table with a quick release handle or allen bolt)
2. Wahlstrom Float Lock Drill Press Vise. Lists somewhere in the vicinity of $200 new from MSC when not on sale -- a bit less for the 9" capacity and a bit more for the 12" capacity. People prefer the quick release version. You can buy an optional clamp bracket that you can use to mount the vise WITHOUT drilling a mounting hole in your table.
3. Lassy tools drill safety vise. I haven't used one of these, and they cost more than the other options. They look really nice, though, and I know a couple of experienced machinists who love them.
I believe all of these have shallow grooves milled into the jaws to (like built in machine vise parallels) to allow you to face drill drill flat stock easily.
Lots of people also like the Heinrich gripmaster cam-locks. Other companies make similar ones, too (dayton, wilton, etc...quality varies...but heinrich's are still excellent). I started out with a pair of the monster 8" ones, which were nice. However, I sometimes drill big holes, and I'd still worry about one starting to spin.
Some people also use a really heavy machining vise and the weight stops the twisting, supposedly. I think this is a bad idea...drill press vises like the first two listed above allow you to through-drill without ruining the vise. I've also seen people use mag-chucks to attach parts and prevent twisting. They seem to do this OK, but I wouldn't want a magnet around all of the chips personally (or around the VFD).
I would also stay away from X-Y vises. I know a couple people who like them, but I find them very restricting. The usual way to work on a drill press is to lay the work out, measure it and mark it (dykem or whatever), center punch the hole locations, then bring it to the drill and let the pilot drill find the center punch marks. Using an X-Y vise prevents your drills from finding the center punched locations. With the Heinrich I showed, you can let it move until the drill has found the mark, then lock it down after. It makes for a really efficient and accurate workflow.