Clow Cards

53 Clow Cards, created by Clow Reed a powerful magician, using a mixture of Oriental and Occidental magic.
Tools: Key of Clow which transforms into the Clow wand also known as the Sealing wand and the Clow Book

54 Sakura cards, 53 transformed by Sakura Kinomoto from the Clow cards and one created by Sakura.
Tools: Key of Star or Key of Sakura which transforms into the Starwand or Sakurawand and the Sakura book or Starbook

List of Clow cards
Arrow, Big, Bubbles, Change, Cloud, Create, Dark, Dash, Dream, Earthy, Erase, Fight, Firey, Float, Flower, Fly, Freeze, Glow, Illusion, Jump, Libra, Light, Little, Lock, Loop, Maze, Mirror, Mist, Move, Power, Rain, Return, Sand, Shadow, Shield, Shot, Silent, Sleep, Snow, Song, Storm, Sweet, Sword, Through, Thunder, Time, Twin, Voice, Watery, Wave, Windy, Wood, Void.

List of Sakura cards
All of the above + the Love which turned into the Hope when merged with the Void card.

Elements and powers
Four Elemental Cards (occidental elements) Windy, Firey, Watery, Earthy
All cards work through the 5 oriental elements - Water, Fire, Earth, Metal, Wood.
Some cards depend on moon power, controlled by Yue, for the others their power comes from the sun, controlled by Keroberos. Once Sakura becomes the offical cardmistress, their power comes from her magic and her star this is why she gets so tired when she uses or transforms them.

Sibling cards and friendships
The cards counteract or react to each other:
Some of the related cards (such as Rain and Cloud) look the same as if they were sisters. Others are twins, such as the Light and Dark cards who counteract eachother but wish to be captured together. Other cards are friends such as Rain and Wood. A cardcaptor must choose the right card to bind another. Depending on the card, it will let itself be captured (Windy, Light,...) or fight until it is caught (Watery, Rain, Ice...)

The cards have emotions
Some more than others. Some cards can be compared to little creatures (the Dash) others like the Mirror, Light and Dark could be compared to faeries and actually speak to Sakura. The cards are designed not only to serve their master but to care for him too (as seen in the final judgment and second movie).

Transforming the cards
Transforming a card drains much of Sakura's energy but as she becomes more powerful she can transform more cards at a time. The last cards to be transformed required Syaoran and Sakura's power together. Sakura can not transform them both by herself. This maybe implies that they will become a team working together against the forces of evil in the future.