Hi Ken and Jane. Hmm.. long list.

First of all welcome to UKY and you are moving to one of the most beautiful parts of the UK! (I am a bit biased, but it is lovely and we also have some of the mildest weather thanks to that gulf stream -granted it can be sunny, rainy, cloudy, windy and even icey all in one day but hey!)
Leave the DVD and video as they are cheap to buy here and you can even buy a DVD that is multiregion and will play US and UK DVD's. You can bring the computer as long as it is 110/220, but I remember from another thread that MAC's might not be. Unless it's a laptop and most of those are. Someone else can help you with that one.
Some people swear by converters. I just got new stuff here.
You can most likely get broadband unless you move to the sticks.
You can get popcorn in Exeter though the mircowave kind is moe expensive here. We just buy it kernals and make it the old fashioned way. You can buy a hot air popper too.
I still have yet to find Sushi or Tex-Mex in Exeter and Plymouth has a Tex-Mex place, but it's not the best. You will either have to make it yourself or go to London. Plymouth does have a decent size Asian store (well two or three) and Cornwall and Devon are home to some of the freshest seafood. I make sushi and rolls when we get the craving.
We have things like Chili powder, cumin, and some Old El Paso things. Flour tortillas and the like can be found at the supermarket. You will find the cans smaller and the prices higher. Decent corn tortiallas will have to be made a home or long life ones can be purshased in London or on two websites of Lupe Pintos or Cool Chili.... both are good.
In truth most things can be found here with time and money. It's just a matter of deciding what it is you will miss and what's most important to you.
Hope that helps! Feel free to post in other parts of the board with more specific questions and also do a search for others.