This page is a work in progress. However below you'll find a little information on what vessel or container you may want to drink from.
What drinking vessel or glass do I use?
There is no almighty laws that determine what you drink Liqueurs from. However sometimes it's nice to have a glass that increases the presentation, especially when serving others. Or on the subject of function, there are several types of glasses which are claimed to increase your pickup of aroma or decrease it depending on what you desire.
As you probably know, smell is a big part of taste. It can affect your whole Liqueur experience in drastic ways.
There are a few factors you can consider, the taste or aroma you will get out of the vessel, presentation and even the material of the vessel.
Taste and Aroma
A Snifter is a glass often used for Brandy, Whiskeys or for tasting various Liquor. The glass has a wide bottom side and a narrow top. A wide bottom provides more surface area for evaporation of the Liquor and the narrow top helps funnel the gathered aroma to your nose as your sipping.
I recommend using a Snifter for tasting Liqueurs as well because many of them have great aroma that you may not pick up using a shot glass, rocks (old-fashioned) glass or any other popular drinking vessels.
Presentation is everything...almost
For presentation and when your guests may not care too much about examining the smell of your Liqueur in detail you can choose something different. A full set of Liqueur or Cordial glasses may be ideal and bring some unification to the whole setting. There are of course many different glassware manufacturers all over the world with everything from very conservative styles to crazy outlandish shapes and sizes.
The picture included in this article is a good example of a interesting "Cordial" glass set. I found it on amazon.com while looking at what is out there.
Psychologically, taste can be affected by presentation. Scientists have studied this and found that when people are in an unusual place or setting it makes the food and drink taste better. Same reason the High-End Liquors and Liqueurs typically have great bottles.
Material and Texture are important
Most drinkers will naturally gravitate towards glass as the material of choice for drink-ware as it does not introduce any flavors, its not porous, and it has a smooth texture with a cool temperature feeling. However you can drink out of whatever you like and sometimes it can really add to a unique party to choose a different material. Many different types of Wood, Stainless steel, Pewter, Stoneware all make a drink more interesting.
Keep in mind the liquor, liqueur or cocktail you are serving and the temperature, color and feel of the vessel.
Where can I find some cool drink-ware?
Honestly, use Google. I don't have any specific sites at the moment that I just love. Amazon.com has a ton of glassware, I use it because its easy, but there are hundreds if not thousands of import sites, tiny shops selling their handmade or hand-blown wares. Try searching with different terms "liquor tasting glassware" "liqueur glasses" "bourbon glasses" etc. I'm sure someone out there has made something specific for your choice beverage.
See the wikipedia article for drinkware that has a nice list of various glass types.