If you have a Steam account, you probably know that playing certain games will reward you with a number of virtual cards. Steam cards can be sold in the Steam Market (prices go from $0,05 to $5 for especially rare foils), they can be traded, and if you collect a game's whole set you can craft them into a badge. Crafting a badge will give you a background and an emoticon (backgrounds and emoticons can also be sold or traded), and raise your Steam level (Stem levels #10, #20, #30 etc reward you with more customization options to make your profile prettier).
Ok, so now everybody knows that cards have value as merchandise or as tools to improve the overall looks of your profile. But what about their intrinsic value?
Here is the thing. Some cards are nothing more than the profile pics of the characters in the game. In my opinion, that's pretty lazy.
But some cards actually show beautiful art. By clicking on them in your "Badges" page, you get a HD wallpaper-sized work of art. I've actually used some of those pictures as desktop backgrounds. I would go so far as to say that some card sets count as virtual artbooks.
Note: the HD wallpaper-sized picture only appears if you either own that card or if you have already crafted the badge. Otherwise, you can take a look at all the pictures here:
Simply find the page of the game you are interested in, then click on the tiny "HD" link on the upper right corner of each card.
Here are some of my favourite cards! Why don't your post yours in a comment? :)