- JLCKicadTools - Useful if using Kicad + JLCPCB's assembly service
- Aisler PCB manufacture and Assembly - Prototype quantity PCBs manufactured/assembled in Europe or the US (2 or 4 layer)
- OSHPark - PCBs manufactured in the US (ENIG only, 4 layer, flex)
- JLCPCB - PCBs manufactured/assembled in China
- PCBWAY - PCBs manufactured/assembled in China
- Altium - How to achieve proper grounding
- found from this twitter post by jonoxer
- Also see What Every PCB Designer Should Know - Return Current Path (with Eric Bogatin) Explanation about return currents for both single-ended and differential signals