Lego, all 3 are Lego mad, even DD14 wants some Avengers set (she has a crush on Robert Downey Jr). DS7 who is a late reader loves Lego as he can usually manage the instructions as they are pictures not words (also means minimal involvement from us. Makes them models once then they seem to always be making them into tall towers and houses 
We also have several sets of Scalextric which are excellent for older children - although the newest is 8 years old, so don't know if they are still as good.
The wooden train sets were good when smaller, although we only had a small amount of Brio, most was Tesco's own brand and just as good.
Sylvanian families still really popular in our house from originals with DD27 to DD9. Even DS7 plays with his sister's stuff.
Can recommend a Wii, especially as they can be bought for less than £50 with loads of games and accessories (try your local selling pages on facebook). Also they each have a DS which have had many hours use.
I have an iphone 3gs, which DD14 will be getting for christmas and DDnearly 10 will be getting her iphone 3g. I will of course be getting a 4 or 4s. Son will have an android tablet. The free apps areexcellent, keeps them occupied for hours and there are lots of educational ones. DS spends ages on a space one looking at different planets and stars. DD9 has some maths apps and also managed to find some english apps in UK english (most are US english). These will all be second hand and be less than £100 each, except mine which will be via Amazon using my Nectar points.
Haven't got much of the playpeople stuff, as went down the Lego route - wanted to have more of one thing rather than lots of different stuff. Also had megablocks when they were small as we were given it as presents - it was always on offer in Woolies. It's ok when new, but goes loose after a while, doesn't last like duplo, but a good cheaper substitute for smaller children.
Other best buy has been the TP 3 swing set with climbing frame on the end. We've had that over 10 years and they play on it every day the weather is good still (which is a shame as we could do with the space, so we've had to convert the underneath of the trampoline into a chicken run). Always a draw for visiting children too.