One of my favourites. ESR have been in the business long enough to know what's what. A good eighty percent of the gadgets on these pages are constructed with components supplied from this friendly company.
I found ESR to be a good source for Veroboard. Also good for capacitors, resitors, semi-conductors, etc.

Another favourite... once you get your head around the £30.00 minimum order thing. Pretty much everything all under one roof, which makes life a heck of a lot easier. Also good for Vero... but their minimum order policy makes it an expensive way of doing things.

Rapid is good for various components but beware of their postal service:- they charge a hefty £8.50 for next-day delivery - only for the item not to materialise until four-thirty in the afternoon. The lousy couldn't care-less attitude of the sales department is probably enough to put most folk off from buying from this company again.

As the title suggest, Technobots cater predominantly for the robotics fraternity. An excellent source of motors and gearings and also a good variety of electronic components.