Ok, there are plenty of cards to buy for Naruto.  I'm going to try and explain the rarities and associated means of obtaining different cards of varying rarities.

This guide is intended for American cards, I'm not sure about other countries.

First, the DOT system.  The bottom roughly middle of a card has any number of dots ranging from 0-3.  0 dots is an uncommon, 1 dot is an uncommon, 2 dots is a rare, and 3 dots is a super rare.  Shiny reflective cards with less than 3 dots are just foils.  The two kinds of foils are wave foils, and rare foils.

In a standard booster pack you're guaranteed one rare, and one foil, or one rare and one super rare (they package it this way so that packs with super rares weigh the same as packs with regular foils).  If the dots at the bottom are WHITE, then the cards were obtained either from one of the very first start decks, or from a booster pack.  The rares from the very first starter decks did NOT have gold text, and were black text.  Newer starter decks use RED dots to detail the rarity (side note, starter deck rares are generally underpriced, as they are very prolific.  I actually got a 3 red dot Chidori for buying someone a fifty cent soda).  Rares have GOLD text for the name.  A card can be Common, Uncommon, or Rare AND be a foil.  These cards are just foils without gold text.  Super rares have 3 dots, and are gold foiled.  In the older boxes (I forget up to which set) you would get 2 super rares out of 1 box, with 24 packs in a box.  Newer sets get you 4 super rares out of a box, still consisting of 24 packs.

And then, there's promo cards with silver text for the names.  These are neither diamond or wavy foiled, but are merely just shinier versions.  These are platinum foils, or just "promos."  These can be obtained from a wide variety of places.  The most common is from a tournament prize reward, but they can also be found in random magazines such as Shonen Jump! magazine.

Finally, there's something called Metal Cards, which are high level rewards for Naruto tournaments.  I'm unsure if these are platinum rares, or actual cards made of metal.  I've been told they're actual cards made of metal.  Sorry I have no further data on the matter.