Here is a list of low-cost PCB manufacturer with online quotation :
WellPCB is a company based in Shijiazhuang Hebei, China. The PCBs are manufactured in Shenzhen, China. File format supported: Gerber, Protel 99se (.pcb), DXP (.pcbdoc) or CAM350 (.cam).
Multi-cb: company based in Poole, UK. PCB are all UK origin. File format supported: Eagle CAD, Target 3001, Sprint Layout, Gerber, ODB++ and IPC-2581.
Beta-Layout / PCB Pool File format supported: DesignSpark PCB, Altium (PROTEL), Target, Eagle CAD, Orcad, UltiBOARD, Proteus, Sprint, Quickroute, EASY-PC, , EDWin, GC-Prevue, PCAD, Boardmaker, Pulsonix, Kicad, DipTrace, Fritzing and GERBER.
eecart: company based in Hangzhou, China. Manufactured in China. File format supported: Gerber 274X , ODB++, Protel and Eagle CAD
DirtyPCB: USA company, with Chinese partner company. Boards are made in Shenzhen China and ship from Hong Kong. File format supported: Gerber and Eagle CAD
ALLPCB: professional PCB manufacturer platform that work with a lot of experienced PCB manufacturers in China. ALLPCB is a topspeed pcb manufacturer in China, specializing in high quality and cheap pcb prototype & production, pcb assembly and smt stencil services online. File format supported: Gerber, Protel 99se (.pcb), DXP (.pcbdoc), CAM350 (.cam) and Eagle CAD (.brd)
Missing manufacturer or any additional information are welcome.