I think it's a fair statement to say that today most of the leading VTL vendors and a lot of the network-attached storage (NAS) vendors are offering deduplication. There are some incumbents and some newcomers. FalconStor and all of the FalconStor partners have FalconStor Single Instance Repository (SIR) options for deduplication. Data Domain has been in the game for a long time. Diligent, same story. It just got bought by IBM and is still working with HDS and is offering deduplication with the VTL.
A few more that offer deduplication -- and there is a longer list than this -- include Sepaton, NEC, NetApp and Quantum. NetApp is later this year and I think it will be available in Q4. If it's not on their product roadmap and companies are sticking with the first generation VTL story with no dedupe, they are very likely to fall behind in the market.
Click here to check out the entire VTL Deduplication FAQ.