British English - American English
adviser - advisor
analyse - analyze
apologise/apologize - apologize
axe - axe/ax
behaviour - behavior
catalogue - catalog/catalogue
centre - center
cheque - check
colour - color
councillor - councilor
counsellor - counselor
defence - defense
dialogue - dialog/dialogue
favour - favor
favourite - favorite
enrol - enroll
fulfil - fulfill
grey - gray
honour - honor
humour - humor
instal - install
jeweller - jeweler
jewellery jewelery
kerb (edge of pavement) - curb
labelled - labeled
labour - labor
liqueur - liquor
licence - license
litre - liter
marvellous - marvelous
metre - meter
neighbour - neighbor
organize/organise - organize
plough - plow
practise (verb) - practice
practice (noun) - practice
programme - program
pyjamas - pajamas
quarrelled - quareled
realise/realize - realize
signalled - signaled
skilful - skillful
theatre - theater
through - through, thru
travelled, -lling - traveled, -ling
tyre (on a wheel) - tire