There are loads of good simulations freely available on the web and
there are some great ones. Here are some of the truly great
These are really extensive and go well beyond the syllabus, the two below are ones that I find particularly useful.
This one is superb, try the 3D view. I use it almost every lesson throughout the waves topic. You can do reflection, refraction, diffraction, interference, doppler, standing waves in fact everything you would like a ripple tank to do if you could just set it up correctly.
This one shows what field lines look like in 3D. You can also see what would happen to charges placed in the field. If you want to make it look like the picture in the book try slicing.
There are some fantastic ones on this site, here are a selection of my favourites. I can't add a direct link since these must be dowloaded (you must also have Java) but you can find them on the site.
Gas Properties
Wonderful. I use it every lesson throughout the thermodynamics course. Notice the man is wearing a space suit. See how he has to push when doing work.
Faradays Electricity Lab
I wish this had current flow instead of electron flow but you can't have everything.
Circuit Construction Kit
The voltmeter is really neat. Gived the idea of pd being from one point to another (I suppose a real one does this too).
Balloons and static electricity
Great for introducing the concept of charge.
A PDF file of all the applets I use in my lessons ordered according to topic