To state the "standard," a traditional Chelsea boot is made of black (or occasionally brown) boxcalf leather, with a leather sole. That said, over time, variations have emerged that are similar to the Chelsea boot, but wouldn't technically go by that name.
There are subtle differences that have cropped up to cater to a contemporary market. Here are some of the basics:
A commando sole (basically a rubberized sole with treads) is common, especially for people who are looking for a Chelsea boot that can handle snowstorms and tough weather.
Jodphur boots share the horse-riding origins with the Chelsea boot, but have a wrap around buckle closure instead of elastic side panels. As mentioned before, for some Chelsea boots, zippers may also be added in place of elastic sides. Even with all this variation, for Chelsea boots, less is more. Keep it minimal, and you're going to be that much closer to an authentic Chelsea boot.
Zip ankle boots are named for the side or back zips that appear in place of elastic to help keep the boots on your feet. It's a less classic option, but equally versatile for a pair of Chelsea boots. While zippers help with fit and flexibility, these boots are technically not a true Chelsea boot, at least to menswear purists. But it's not wrong to kick around in a pair either, plenty of times they offer a cleaner shape than traditional Chelseas.
Broguing is the technical term for the "wingtips" on your wingtips. The perforated designs are all a matter of personal preference, but they're not necessarily ugly—just not as popular as the smooth silhouettes you see on stylish dudes all over the place these days.