I've had my car done. I think it's necessary to do in Canada, a lot of people don't though since they lease cars for 4 years and dump them.
There are so many companies that offer it here. I really don't know who is best. One thing that I find to be important is to find one that uses an amber colored product as opposed to a black color so that when it creeps you don't have an ugly mess.
qship96 is right. In Canada Rust Check and Krown are very popular probably because they are everywhere. The owners of both those companies used to be partners once upon a time and had a fight. They split and now they are competitors.
There is another company
http://www.corrosionfree.com/index.htm
They claim that their product is clean, clear, drip-free, solvent-free, odor-free, non-toxic, a super lubricating metal conditioner with creeping and penetrating benefits - all in one formula.
It is not a sealant that traps moisture, or an oil spray that rots rubber, damages plastic and tend to be messy and drippy. It contains active moisture displacers that last up to 18 months. Because it is clean and transparent you can actually see it preserving the original "factory new" appearance. It does not dry out, chip or peel off and its lubricating benefits continue indefinately."
There is also:
Rustblock® Diamond·Kote CounterAct Corrosion Protection