It really depends on the mood, the ambient noise and the complexity of the tasks. It could go from very soothing soundtracks to extreme metal, with many kind of jazz or math-rock in between ;-) Some samples:
When there's more ambient noise, then the playlist takes a more metalish atmosphere, these days with sludge like Lumberjack feedback - Dreamcatcher (2 guitars, 1 bass, 2 drums, no vocal), and when I really need to isolate from the environment, I then build a sound wall around me, with stuff like Gojira (The live Aux Vieilles Charrues for instance is great), Gojira - Silvera or Meshuggah Meshuggah - Spasm
And many many other things, I could keep the thread running forever ;-)