Apart from those menntioned (Conrad - huge selection, but lengthy delivery (expect to wait for a week), or Distrelec - huge selection, next day delivery (never failed once))
There is also http://www.play-zone.ch/en/
(arduinio kits and electronics) and http://www.boxtec.ch/
also sell electronics kits (Velleman) and Arduino stuff, but not single components. Delivery is free (and next day)
I noticed that with Playzone, Boxtec, that the quality of some of the components is not so good - e.g. resistors with extremely thin leads, that seem to resist making a good contact in the breadboard, etc.