I brought my desktop speakers over and a proper step-down transformer (from Radio Shack). They worked just fine, and I've never had a problem with the voltage, but I do regret lugging them through two airports and a train station when I could have spent a few pounds and bought a new set here.
The same goes for most small appliances--I can't imagine anything that's worth the bother of bringing it over that you can't buy in Argos, Tesco, etc. Unless you have specialist cookware that you can't live without, I wouldn't bother with that either. Most ovens are too small, as people have discovered, and you can get reasonably good stuff from Tesco, Marks & Spencer, etc. TK Maxx often has high-quality cookware for cheap (the one in Newcastle had a big selection of Le Creuset for less than half price recently, for example), and so on.
I brought a lot of miscellaneous computer cables and hand tools which I could have easily replaced for very little money.
The first aid kit, toiletries, and over-the-counter medicines were mostly a waste of space, too. The only thing I haven't found here is naproxen (Aleve), and it's a little bit annoying to be restricted to buying 16 tablets of aspirin at a time (I have a lot of headaches!) but it just goes on the grocery list with the milk now.
Like everyone else, I had far too many clothes. And even though I'm plus-sized and its not as easy for me to buy stuff that I like anywhere in the world, it hasn't been any more challenging here over all than it was at home. I didn't bring anything in particular that wasn't used, but I realized recently that I had 7 nearly identical pairs of blue jeans. Surely two would have sufficed!