Synth music is a contemporary style of music using the latest in technologies such as Synthesiser Keyboards,Vocoders etc.. Leading musicians in this field include the likes of Vangelis,Jean Michel Jarre, Kraftwerk, Tangerine Dream, David Arkenstone, Gandalf, Ian Boddy, John Dyson, David Wright, Robert Fox,Yanni,Suzanne Ciani,Enya,Jan Hammer,Kitaro,Tomita,Wendy Carlos, Klaus Schulze and the list goes on...Other favourites include Bekki Williams, Andy Pickford, Mark Dwane, Mars Lasar, Iotronic, Claudio Merlini,2002, and Robert De Fresnes.
What do you need to create your own Synth Music? It varies from either buying a Music Keyboard with a builtin 16 track sequencer,speakers and hard disk/floppy disk, or if you already have a computer such as a PC/MAC, you can buy music creation software by companies such as Roland,Steinberg, and others. Alternatively you can combine both and more to create your own music studio, if you have the money.
You will find that you can buy either Online through places like amazon or your local retailer like argos, but the high-end synthesisers, you normally have to buy from a specialist dealer (e.g. DV247.com or Professional Music Technology or Gear4Music) for brands such as KORG,Roland,Yamaha,MOOG, Novation, Nord, Sequential, Modal, Waldorf, Behringer, Arturia etc...
In regards to Vocoders you can get them built in with your Korg microKORG XL + Synthesizer/Vocoder or Arturia Microfreak Vocoder Edition or Novation MiniNova Synthesizer, or you can buy software such as IL Vocodex and a Mic.
In regards to Theremins they can be in the form of hardware (such as Moog Etherwave Theremini Miniature Theremin ) or VST Instruments such as Spook Keys/Super Spook Keys.
Another new development, is that Behringer have started doing new versions of old classic synths, such as the Korg MS20 (Behringer K2), Moog model D, Arp Odyssey, etc.. Plus some completely new synths, such as the Neutron.
You can add instruments to most software in the form of VST/AAX(newer Avid format) from various companies such as Steinberg, Tone2, Image Line,Arturia,UVI, Native Instruments, etc...For sampling there is Halion, Kontakt, etc...
Newer versions of DAW's are now starting to support MPE.