Athame
It's pronounced a-THAW-may or ATH-amay, not A-THAME. The athame is a ritual knife or dagger, usually double-edged with a black handle. The knife represents Fire, but is never used to cut anything physical. An athame is often used to cast a circle. It's symbolic only and many suggest you dull the blade to prevent any accidents.

Chalice
Your chalice (or cup) represents Water. Altar chalices are typically a stemmed goblet style, but any cup, glass or mug will do. Your cup is used to hold the water or wine for drinking at the end of a ritual or circle.

Wand
Most people think of wands as long wooden branches with a big stone on the end. Your wand can be any material you feel drawn to (wood, metal, bone). Your wand is the tool of Air, and is used to direct energy during ritual. Wands tend to be the one tool that most Wiccans are likely to make themselves.

Pentacle
Your altar pentacle can be anything from a simple pendant, to a large table-top platen. The pentacle represents Earth, and you use it to cleanse or consecrate other items on your altar. Typical pentacles are metal, ceramic or carved from wood.

Cauldron
The cauldron represents Water, like the chalice. Most Wiccans don't actively use cauldrons but keep one for the symbolism and the sheer 'witchy-ness' of it. Cauldrons are cast iron pots, usually pot-bellied in style. If you cannot find a true cauldron, other bowls or pots may be used. Though it represents Water, many rituals also call for small fires to be burned in the cauldron. If you plan on doing this, make sure to have a cauldron that can take the heat.

Bowl of Salt
You can use a bowl of salt to represent the Earth, rather than an altar pentacle. Salt is used to cleanse other tools, crystals, jewelry or any item that may pick up negative energy. A small bowl of salt (coarse sea salt is best) is simply kept on the altar.

Other Items
Candles - Represent Fire, and some people keep a special pair of candles to represent the God and Goddess
Bells - Used to mark points during a ritual
Censer - For burning incense (Air)
Sword - Just a longer version of the athame. Not very practical for the solitary Wiccan
Boline - Curved knife for harvesting herbs, not really necessary for most people
Incense, crystals, statuary - Not really tools, but handy and attractive things that many Wiccans like to display on their altars.

You may never use all of these tools on a regular basis, but you may come across a spell or a ritual that you want to do that requires one. If you don't have a tool, you can always improvise, or keep your eyes open for your next magickal item.