Exterior concrete comes in a number of different types, making its protective options vary significantly. As driveways are the biggest category of exterior surfaces, we will spend primarily address their protection, though all of our suggestions can work for any other exterior concrete surfaces.
Driveways tend to either be made from gravel/dirt, brick pavers, or concrete. The first option cannot be sealed, as it is not concrete. However, the latter two are important to protect if you dont want to have to replace your driveway after only a short period of time.
If you have a traditional concrete driveway and live in a colder climate with regular to heavy snow in the winter, you should use a silane/siloxane blended sealer, such as Siloxa-Tek 8500. In the winter most roads are plowed and salted regularly, with that salt becoming a permanent feature of your car and its tires. It is better to use a product like Siloxa-Tek 8500 that will block out the salt, protect the concrete from freeze-thaw cycles and prevent organic growth. If you are looking for additional added protect from staining of leaves, oils and grease the best products to use would be the Siloxa-Tek 8505 (water based) or the Siloxa-Tek 8510 (solvent based).
If you have a traditional concrete driveway and you live in a warmer climate where it is unlikely or uncommon to find snow, you can use the Lithi-Tek 9500. The 9500 offers the best level of penetrative protection from such problems as water solubility (water will bead off the surface) and other forms of weathering, and it will not scratch or peel off over time.