[WishIWasThere]

California is a great place to visit! But, with 8 days Id stick to Southern California unless you want to fly to Northen California. TO fly in there are 3 main airports within an hour and a half from Disney (there are several smaller ones as well but I never flown into any of those) they are San Diego (my personal favorite), Los Angeles (great too) and Ontario (a smaller one but still good). LAX would probably be the cheapest.
The entrances to the two parks are start across an open area from each other, if you stand at the entrance to one you can see the entrance to the other. It might take 30 seconds to a minute to walk back and forth. Downtown Disney is about a minute walk from either entrance (or two minutes if you walk slow). If you have never been to Disneyland I would take four days to see it. That way you can go slowly, enjoy yourself and see the shows/parades.
As for other things to see/do, it depends on what you like to do. Theres Six Flags, Universal Studios, and Knotts there. If you like dinner shows Medieval times is near by. If you like animals you can go to the San Diego zoo or wild animal park. Then theres beaches, parks, etc. If you go in the winter you could visit someplace like Big Bear where the snow is, theres also some ski slopes near there (don't know too much about them though, I never skied)