TV, VCR, DVD: buy it in UK - the system is entirely different. Be aware that the UK is Region 2 for DVDs while the US is Region 1, so you would have to buy a player that will play both indefinitely.
FM receiver: be sure that it covers the right frequency range - about 88 to 108.
Computer: you can easily replace the power supply, but watch out for peripherals which may not like the UK mains.
Anything that runs on mains electricity: be sure that it can run on UK supply - 230-240VAC 50Hz. Buying new external power supplies or voltage convertors for all your gadgets becomes expensive.
All in all, even though the UK tends to be rather more expensive, the hassle of trying to run US equipment in the UK is hardly worth it. I have sold many voltage convertors to US citizens living temporarily in the UK, and most had already blown up at least one costly piece of kit.
Customs Duty: Beware of buying new kit in the US and bringing it straight to the UK - you will probably be charged import duty and VAT (which, with shipping costs, will more than wipe out any savings). As a rough rule, you must have lived outside the UK for more than 12 months, owned and used the goods for more than 6 months, and do not dispose of them for 12 months after importing them. See
http://www.hmce.gov.uk/forms/notices/3.htm#P254_18043