I have a poll here which showed a pretty even distribution until Sparkfun decided to send all their fans at the site: http://mightyohm.com/blog/2009/01/poll-who-is-your-favorite-prototype-pcb-vendor/

• Camptech II Circuits
• PCBWay(Cheap and high quality pcb. $10 for 10 pcs)
• OSH Park (formely known as BatchPCB)
• Technotronix PCB Manufacturing
• Custom Circuit Boards
• Gold Phoenix
• PCBCART
• Bittele (aka 7pcb)
• Olimex
• APCircuits
• Wonderful PCB
• Barebones PCB
• PCBFabExpress
• DorkbotPDX PCB Order - (Open to everyone not just dorkbotpdx people)
• seeed studio
• Advanced Circuits
• Asian Circuits
• Flash Line Electronics - They have a $10 for 30 sq in. and $20 for 60 sq. in 2-layer special.
• San Francisco Circuits - They offer a hobbyist special
• PCB Assembly

Other web sites with long lists of PWB fabricators:

• PCBWay(Cheap and high quality pcb. $10 for 10 pcs)
• Ladyada's "PCB Cost" Calculator -(its a good way to get a idea of cost, but don't count on it being exact)
• Open Circuits wiki: PCB manufacturers
• Massmind: PCB fabs (it's almost a wiki)
• DMOZ: PCB manufacturing
• Chiphacker: moderately priced 6-layer PCB fab?
• Chiphacker: Cheap PCB manufacture (it's almost a wiki)
• Ladyada's List of PCB Providers

• Sparkfun solder paste stencil tutorial
• OHARARP - Kapton stencil, 8.5×11“ max, $25 per sheet + shipping
  • 3.5 mil thickness.
  • Writeup on using these stencils: http://www.circuitsathome.com/production/on-reflow-soldering
  • Has anyone used them?
• Pololu - Mylar (plastic), 24×12” max, $25 for 4 in sq. + $1 for each additional square inch
  • 3 or 4 mil thickness
  • Christian reported having problems with too much paste on fine pitch components. Not sure what thickness he was using.
• OSH Stencils

• Ladyada test fixture howto
• Cheap pogo pins - Datasheet
• Or search for “P75-LM pogo pin” on eBay