Wood

Holz-Possling in Berlin, expensive shipping, but good, cheap[er] wood

Metal

Gemmel Metalle in Berlin, minimum order amount ca. 40€
Ebay you probably know where to find this...

Electronics

Reichelt fast shipping, big selection
Berrybase
Voelker
Conrad
Roboter-Bausatz
Segor in Berlin, suprisingly large selection

Screws

schraubenking
rosenthaler schrauben
berliner schrauben

Laser Parts and sheet metal

laserteileonline Cheap, small quantities
Tailorsteel High Quality, larger Projects

PCBs

Aisler Germany, fast turnaround
PCBWay Overseas/China, cheap, long waits
jlcpcb Overseas/China, cheap, long waits