Ones I heard of:
GB AIRWAYS
A321s G-TTI_ (T-hree T-wo/T-wenty 1)
A320s G-TTO_ (T-hree T-wo/T-wenty 0)
BRYMON
DHC8s G-NVS_ N-oise & V-ibration Suppression (or something similar) [DHC8Qs]
BRITISH AIRWAYS
B777s G-YMM_ Y2K / Year 2000 in roman numerals
Older ones:
AIR ANGLIA
F27 G-SPUD - for Spud Murphy, former chief pilot (I believe)
F27 G-STAN - for start of AQ ops from Stansted
AIR EUROPE
Regd first half dozen B737s for founding members:
G-BMEC for Errol Cossey
G-BMHG for Harry Goodman
G-BMOR for Martin O'Regan
G-BMSM for Stephen Matthews
G-BRJP for Roy Phillips
G-DDDV for Capt Desmond de Verteuil
Can't think of any others off the top of my head...
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Lizard