Lithium-ion batteries have become popular over the last couple of years and slowly replace lead-acid batteries. You might consider investing in them, if you haven't already. They can be counted as deep-cycle by default and therefore they're perfectly suited for solar panel systems.
Lithium-ion batteries are more expensive, but lighter, more efficient, require less maintenance than lead-acid batteries and have a higher DOD. There's no need to water them and they are less susceptible to partial state of charge. However, just as lead-acid batteries, they don't like high temperatures and prefer not to be fully discharged. Don't put anything flammable around them. If you need a recap on different types of deep-cycle batteries, check out our article.