Having spent more time than is healthy researching this particular subject myself, this, I believe, is a reasonably definitive (but no doubt incomplete) list of synths and keyboards used by the band, in roughly chronological order:
1. EMS VCS3 with pitch to voltage converter - Del Dettmar
2. EMS Synthi AKS - Dave and Nik both got one of these in 1973. Nik's was usually used by Simon House on stage. After he left the band, Nik took his to Inner City Unit where it was played by Fred Reeves. During one particular gig, Reeves is alleged to have thrown it at Nik, and it sustained some damage when it hit the stage. Sold shortly after to Norman Fay then re-sold on the VEMIA site a few years ago, restored to full working order, and still with its ICU paint job.
Dave has kept his and used it on many, many recordings, retiring it from stage use in 1981 after the case got broken.
Tim Blake used 2 heavily modified EMS Synthi's, which he had from his Crystal Machine days - one of them is a very early serial number 00007. These were sold in 2004.
Del also had, and still has, a VCS3 and a number of Synthi A's.
3. Mellotron 400. Simon House played one of these on stage and on records from 1974 to 1976, usually with the strings or choir tapes (D-Rider, Psychedelic Warlords, Paradox, Golden Void, Chronoglide Skyway etc. Reported as being 'unreliable'. He replaced it with:
4. Logan String Melody. As heard on Robot on PXR5. Sold via Hawkfan.
5. Korg 700. Heard on many, many recordings and on stage from 1974 to 1984, used by Simon House, Steve Swindells and Dave Brock. This one came up for sale in a Cornish newspaper in 1995.
6. Moog Minimoog. In the mid 1970's, major studios sometimes had a resident Minimoog, and Simon House took advantage of this on Astounding Sounds and Warrior.
Tim Blake also had his own Minimoog, a very early one which he bought from Manfred Mann.
7. RMI Electro-Piano. Simon House, 1974 – 1978 (especially on Quark album).
8. Audio Generator. Custom built, used on stage by Dave and Bob (1976-1978).
9. Yamaha CS-80. Steve Swindells, Hawklords.
10. Roland System 100. Tim Blake 1979/80 (New Jerusalem bass sequence)
11. Korg Polyphonic Ensemble. Tim Blake.
12. Korg Lamda. Tim Blake and later, Dave Brock (“syrupy string sounds”).
13. Korg MS-20 and SQ-10 sequencer. Dave Brock 1980 – 2008.
14. Roland SH-09. Dave Brock 1981 (Church of Hawkwind)
15. Roland Jupiter 4. Harvey Bainbridge 1981/2.
16. Roland Jupiter 8. Dave and Harvey both used JP8’s big time, 1982 onwards.
17. Korg Polysix. Dave, 1982 to present.
18. Roland Guitar Synth (not sure which model). Huw Lloyd-Langton (Dragons & Fables).
18. Roland JX-3P with PG-200 programmer. Dave, late 1980's to present.
19. Casio CZ-1000 and CZ-101. Dave and Harvey, mid 1980's to about 1992.
20. Casio FZ-10M rack mount samplers. Dave and Harvey, mid 1980's to about 1998. Think Harvey also had a Roland sampler.
21. Korg M1, M1R and M1REX. Dave and Harvey, 1989 onwards.
22. Roland GR-50 Guitar Synth. Dave, 1990 onwards, using GK-2A pickups fitted to his guitars (especially on Electric Teepee)
23. Roland Juno 60. Alan Davey mid 1980's to about 1992. Swapped for:
24. Roland Jupiter 6. Alan, 1992 to 1997. Used to belong to Fields of the Nephilim, and given a custom dayglo paint job by Alan Arthurs.
25. Korg Wavestation EX, Wavestation AD and Wavestation SR. Alan, 1992 onwards.
26. Kawai K4. Alan, 1991 – 1997 (Blue Shift etc).
27. Korg 01R/W. Dave, early 1990’s onwards.
28. EMU Proteus series. Dave, mid 1990’s onwards.
29. Roland SH-101. Richard Chadwick.
30. Roland JD-800. Richard Chadwick.
There are of course a few gaps - for example, does anybody know what Paul Hayles and Keith Hale played?