Yamaha AN1x

I love this synthesizer.  It has a rock solid MIDI implementation, and it is fairly easy to program.  Essentially, it uses modern digital technology to mimic an analogue synthesizer.  It can sound a little clinical compared to the more organic sound of a genuine analogue synthesizer, but it is totally reliable and does not go out of tune as it warms up!  It includes quite a nice arpeggiator that I can apply to sounds from other modules, and a good varied range of filters, so I can get some really retro squelchy sounds.  The keyboard is quite nicely weighted, for a relatively inexpensive synth, and touch sensitive.  It also transmits aftertouch.  Altogether great fun. 

Yamaha MU80

A basic general midi sound module I bought in 1994, with lots of additional sounds in the Extended GM sound banks.  Some great; some really cheesy.  It has massive 64 note polyphony, with two MIDI ports with 16 parts on each.  It is possible to build some amazing multi-layered backgrounds. 

Plenty of effects, two of which can be applied simultaneously, and reasonable filters though they are nowhere near as strong as the An1x.  It is also possible to plug-in a microphone (but no phantom power) and/or a guitar or a line source, and apply effects to the sounds while mixing it into the midi sounds.  Useful for my Control Synthesis DB9 which has no built in effects.  Very easy to program via Midi.  The first sound module I bought, it is a stalwart that will never set the world on fire.