You want a glass that has a smaller diameter at the lip than it does at the base. Something that is feminine in shape. A big part of tasting is the information you get through your nose and a feminine/tulip shaped glass will hold the aroma in the glass better than a wide-mouthed tumbler. You want something like this:
That's industry standard, it's what is used everywhere from distilleries in Kentucky to house parties hosted by those too-serious bourbon men with their silly pocket squares and bow ties. They're very durable. If you like ice in your whiskey, the standard Glencairn like above won't work, but glasses are made in that shape that are bigger. These are on Wine Enthusiast's website, set of 4 for $39.99:
If you don't want to shell out $5-20 for whiskey glasses, a stemless wine glass from Costco is perfectly fine. Really anything that closes in at the top. On an unrelated note, when you nose whiskey, best thing to do is get your nose over the glass, and as much of your mouth as possible with your mouth open. Then, instead of taking a deeeeeeeeep breath in through your nose, take several sniffs, like short bursts. Imagine a dog sniffing around the ground for information. The dog doesn't take a really deeeeeeeeep breath through her nose, she takes a bunch of rapid sniffs. That's the best way for her--and our--noses to get information, constantly refreshing and reloading to detect what we missed in the last sniff.
Stems are unnecessary for whiskey, good for little more than affect. The biggest benefit of a stem for a glass of wine is to keep you hands off the bowl of a chilled glass of wine. With whiskey, warming it up via the heat coming off your hands is not only good, it's desired. Certain aromatics are released. Many tasters will pour a whiskey and let it sit and air out for as much as 20 minutes before tasting, there are a lot of weird habits/beliefs people have but cold whiskey will always = not fully tasting the whiskey, esp. if you shock the whiskey with ice.