You know about adenine, thymine, guanine, cytosine. Now get used to SICS and MMO2.
In this JACS article published this month, researchers at the Scripps Institute reported the identification of these two artificial bases. They are efficiently incorporated during in vivo DNA synthesis by the Klenow fragment of E.coli DNA polymerase and pair together with high fidelity.
At the moment the applications for these new bases are are limited mainly to providing new building blocks for the in vivo synthesis of DNA-based nanostructures. However, work is ongoing to incorporate them into living cells and make them code for specific amino acids. Although it is far from clear whether this can be done, if achieved it will lead to some new, very powerful tools for protein engineering.