British English to American English: Letter I
Iced lolly Popsicle
Icing Frosting
Icing sugar Powdered sugar
Idealise Idealize
Identity/Identification parade Line-up (police ~)
Idolise Idolize
Ill Sick
Immersion heater Water heater
Immobilise Immobilize
Immortalise Immortalize
Immunise Immunize
In (Britons live in a street) On (Americans live on a street)
Inc Inc.
Indicators Blinkers
Individualise Individualize
Industrialise Industrialize
Infant school kindergarten
Inkpot Inkwell
Inland Revenue IRS (Internal Revenue Service)
Insure Insure
Inquiry Investigation/Inqiry
Industrial action strike action
Industrial estate Industrial park
Industrialisation Industrialization
Industrialise Industrialize
Innings Inning
Initialise Initialize
Instal Install
Installed Installed
Instalment Installment
Instalment plan Layaway/Hire Purchase
Instil Instill
Institutionalise Institutionalize
Insulating tape Electrician's tape
Integral function Entire function
Intellectualise Intellectualize
Interior designer Decorator
Internalise Internalise
Internationalisation Internationalization
Internationalise Internationalize
Interval (theatre) Intermission
Inverted comma Quotation mark/Turned comma
Invigilator Proctor
Ironmonger Hardware store
Issue with (~ new passport) Issue with (not used in US)
Italicise Italicize
Itemise Itemize
Have I missed anything? Send in your American/British differences now.