First up- Tarot!
My favorite! Ok so the basic structure of Tarot is 22 Major Arcana cards (which usually represents big central themes in one's life), then the 56 Minor Arcana cards. Now the Minor Arcana cards have 4 suits: Wands, Cups, Swords and Pentacles. Each suite has an Ace-10 card, then a page, a knight, a queen and a king. Each suit has a general theme (like Cups is usually love and relationships, Wands, work and life passion, etc) and each number represents different things too. Tarot can be read right side up or some readers read reversed, which means that they read cards that come up in the reading that are upside down. Not every tarot reader will do this, and that is ok. It doesn't mean you are getting any less of a reading or that that reader is not skilled. The most common deck is the Rider-Waite-Smith deck, which is what all other decks are modeled after. You may also run into the Thoth deck, basically Aleister Crowley's take on the RWS deck (if you don't who he is, look him up, he's a very interesting read). One great thing about Tarot decks is there is a deck for everyone! You will find all types of different themed decks, mermaids, baseball, homosexual, alien, steampunk, Celtic, Brazilian, and pretty much any other thing you can think of. If you want to see some examples head on over to aeclectic.net and you will see thousand of different decks.
Lemormand is a system of 36 cards that are wonderful for fortunetelling. Clover, sun, stars, etc. The cards are usually a simple one word noun. These cards are named after a famous 18th century French card reader, Marie Anne Lenormand, who is said to have read for Napoleon and Josephine. The spreads that are used with the Lenormand are very different than tarot. You would usually read them in a line, relating each card to the next. Also, you usually read them in pairs, not singularly. For example, in tarot you can read one card, but in Lenormand, it all about combinations. Lenormand is quickly becoming more and more popular! Don't be surprised if you start seeing more and more readers using them!
So oracle cards are cool because they are kind of whatever you want them to be. I have three oracle decks, two has 52 cards, and one has 44. Oracle cards mean whatever the author wants it to mean. Many people use them to read, but I like to pair them with my tarot cards because these cards usually have very general themes and it can be hard to get super in depth with them. None the less, you can still have a reading with it. There are many different oracle decks are the first person who comes to mind who makes a lot is Doreen Virtue. She has several oracle decks and they are all very beautiful. But there are tons of different oracle decks to choose from. All different types of themes can be found in oracle cards and they can be a great companion to Tarot or other cards
Last but not least...playing cards!
The playing cards I'm talking about is the deck commonly used to play games like poker, go fish and such. Now I have to say I know the least about these but everyone has probably used or seen a deck of playing cards in there lifetime so I don't think I have to explain this too much. Many people use playing cards to read. I have see this a lot in the Afro-Caribbean and Roma (more commonly known as Gypsy) community. The first people to use playing cards were the Roma people in Europe about 600 years ago and since then the system has gone all over the globe.
So have I missed anything? And other card systems you guys read with? Let me know!