Hmm, let me think, in no particular order:-
Access to PDP-11s and IBM System/370 machines by sneaking into Cambridge University's labs.
ZX80, ZX81, Spectrum, Spectrum+, Spectrum+2 (never had a +3 or QL)
Jupiter Ace (program in Forth)
BBC Model A, Model B, Model B+, Master, Compact
Oric 1 and Oric Atmos
Acorn Electron
Dragon 32
Archimedes A310, A3000, plus various others
Commodore 16plus4 (with 1541 disc drive), Commodore 64
Amiga A500, Amiga B2000 (with Janus PC card)
Atari ST
RM 380Z and 480Z (Robot Arena was excellent!)
PCW 8256 and 8512
Mac (][/IIse/Mini/G5/etc)
PCs all the way from the old XT/8086
Various Sun/AIX/HP-UX machines (from SunOS 4.1.4_U5, AIX 3, HPUX 8 days, so about 1992)
This includes:
Z80, 6502, 68k, x86, ARM, Sparc assembly to varying levels (ARM is still my favourite).
Linux 0.99-pre13 kernel and the 10 floppy MCC distrib based on 1.0.8 kernel.
UNIX: HPUX/AIX/Linux/SunOS/Solaris/zOS/zLinux
Other OSes: AmigaOS, CP/M (PCW8256 and the 380Z and 480Z), DOS, GEM (my eyes!), Windows 3.x and onwards, MacOS from System 6 onwards
Shame I can't get on any of the big machines we produce at work