Farnell: Good selection of individual electronic components in the UK, but smaller suppliers may be cheaper for some popular items.

CPC: Sister company to Farnell. Good for tools, general electrical and hobby electronics. Again, some items might be cheaper elsewhere.

Bitsbox: Basic (traditional) components for hobbyists. Low delivery charges and good service.

Proto-PIC: Scottish company selling hobby electronics, robotics, kits, etc. Discount available for members.

Phenoptix: UK-based hobby electronics. Quick delivery with a low-minimum order value.

Sites with free samples. Some require a student email address.

Microchip: PIC processors, EEPROMs, and a wide variety of other digital electronics

Texas Instruments: Analogue and digital semis, sensors, etc

Analog Devices

Hobarts: Laser-cutting materials.