It does look a bit like the very early stages of early blight, but it could also be bacterial (such as bacterial speck). My plants have had this before when they've been exposed to cool and rainy weather for a while.

It may have been necessary to remove the leaves eventually, so don't worry too much. Tomatoes are pretty much unstoppable and they will put out new foliage. More than that, however, I would use an anti-fungal product regularly, especially if you live in a humid area.

If you want to grow organically, use a copper-based formula. Copper will also help if the problem is bacterial in nature. I would start out with a copper based formula for now, just in case it's an early bout of bacterial speck.

If you're not concerned about growing organically, you could use daconil (Chlorothalonil), which is solely for preventing fungus-based diseases and one of the most effective products available to home gardeners.

Whether you use one product or both (I will use both when disease pressures are high), make sure they are of the strength appropriate for vegetable gardens, and follow label directions. These products are marketed under several brand names and are available at garden centers just about everywhere, including box stores.

Anyhow, this is just general advice, and be aware that the home gardener does not have access to any treatment that will kill existing infection. The products mentioned above are preventative and will not eliminate an infection from an already-diseased leaf. They are used to keep the disease from spreading to other parts of the plant.

I must admit that I have some sort of weakness at diagnosing via photos. If someone has a different diagnosis, I hope they straighten us out. :-)