Farnell
One of the world's largest catalogue distributors of electronic components and industrial products including capacitors, transistors, resistors, diodes, fuses, integrated circuits, semiconductors and transformers.
http://www.farnell.com/

Mouser Electronics
Electronic component parts distributor, order on-line, same-day shipping, no minimum order. Products includes semiconductors, connectors, embedded, capacitors, resistors, inductors, relays and sensors.
http://www.mouser.com/

Rapid Prototype
A competitive US manufacturer for rapid prototyping and silicone keypad components.
http://www.sitech-corp.com/