Thought I'd chime in since I've been a working theatre actor and props master for a number of years.
The store bought beards are typically made of human hair, but they're somewhat tough to deal with. And they always look strange close up. They're meant to do well on stage, with distance. The plus is they're hand ventilated on french lace (also called theatre lace) and can be reused, and with the right amount of care and patience, they can be styled well too.
If you're doing something for a night (party), or for a photo, I would suggest hand laying crepe hair, as was suggested earlier. It takes a bit of time, but it's not too difficult to learn, and you can really get a good look with styling. There are various resources out there for how to do it, but I would suggest picking up Richard Corson's STAGE MAKEUP (I think it's in the 8th or 9th edition now)- always a great reference to have on hand and is considered by many to be the bible of stage makeup, and it has tons of information that is also applicable to TV and screen work. Some of the best Makeup FX guys in the business started with this book. Look into it!
:cool