Aluminum is one of the most versatile and often-used metals in construction, and is also relatively inexpensive for the strength that the metal provides. Because of this, most do-it-yourselfers find themselves in the position of needing to cut aluminum at one point or another, and when that point comes, it's important that you know exactly what your options are as far as cutting tools.
Because aluminum is relatively thin--compared to metals like steel or iron--it can be cut through by your standard wood-cutting saw, with one caveat: The wood saw needs to have a carbide blade, rather than your standard tooth-blade wood saw. The heavy carbide blade will be able to grind through most types of aluminum with little fuss--although be warned, there will be a significant amount of sparking from the metal, and you will need to keep the blade lubricated with something like WD-40 to keep it from jamming in the metal.
The go-to tool for cutting most types of metal, the angle grinder is essentially a small hand-held circular saw with a heavy grinding blade rather than a cutting blade. It is not recommended, however, that you use the angle grinder for cutting through long panels of aluminum, as the going will be slow, and the grinding wheel will eventually wear down after use. Angle grinders are also useful for cutting grooves or shearing off jagged edges.
While it may sound like something out of Star Trek, the plasma torch has actually become one of the staples of cutting most types of metal--especially metals like aluminum, which cannot be cut with standard cutting torch because it does not contain enough fuel for the oxy-fuel torch to burn through. Hand-held plasma torches are expensive, but cut through any conductive metal quickly and efficiently. If you're going to be working with aluminum a lot, a plasma torch would likely be a good investment.
Metal snips are like a cross between pliers and scissors, and are designed specifically for cutting through relatively thin sheets of metal. Metal snips are recommended only if you have a small amount of cutting to do, as they will eventually tire out your hand, and are also among the slowest of the tools when it comes to the actual cutting of the metal.