I think Tim Blake was using Minimonsta as his main fx synth when he was with Hawkwind most recently, until he took a sabbatical last year to revamp Crystal Machine for a remastered release for it's 40th anniversary. Usually controlled from a theremin using a CV to MIDI convertor to drive the softsynth. Sounds very, very good indeed, and I don't often say that about software analogue synth emulations.

At one point Dave Brock had a Roland of some sort and at the most recent gihs I've seen a keyboard workstation of some sort.

I doubt an EMS has been present for some time, certainly not on stage at any of the well over two dozen times I've seen them over the last six years or so. Really any voltage controlled (so no stepping) synth with a resonant filter plus shedloads of echo and chorus or flanging will get you pretty much there. Even a plain Korg Monotron and a delay can do a very good job.

There's a range of options discussed here (as pwalpwal noted above).
 
Cynthia, the first suggestion, is free, runs in Sonar 64 bit, and can be used as an instrument or FX.
I've used Cynthia (as an FX) to try and get the sound of The Who's "Won't Get Fooled Again".
I can't say I was completely successful, but it's a complicated bit of kit (at least for me), and it's hard to find a good Lowrey organ simulation to drive it with.
 
Cheers, Peter.

thanks all