PCB Manufacturers

UK

Screenbond 1 and 2 layer, low tooling cost, can do 24hr if you can afford it.

Stickleback They have a prototype service via their Ebay shop

SMT StencilPolyester stencils
DarkmassPolyester stencils
TecanStainless stencils, screening cans and photochemical etching
Spark Laser
PCB Train

Lueberg Large PCBs up to 1200x3000mm

PCBCart Long established Chinese supplier, with wide range of options at good prices, even after shipping costs.

Eurocircuits Wide range of prototype and production services including aluminium, also stainless solderpaste stencils.

PCB-Pool Pooling service, with free stainless paste stencils