Hi tofo,
Just make shure you order on Non Inductive versions.
As an example the HS Series (Aluminium Housed) from Ohmite has the HSN being "N" Non Inductive. They say it "complements Ohmite's Military grade 89 Series as a lower cost (commercial) alternative". This series goes to 250 Watts - HSN250.
Sometimes they use the N in the middle of the part number as in XXX N XXXXX.
As for another brand from TYCO HS Series they use the N in the beginning as for NHS - Low Inductance. You have them from 10W to 300 Watts.Also ARCOL (England)-- you can buy from www.elfa.se -- brand uses the same NHS-XXXXXX ordering system.
The prices go in between 6/7 € each (for 50W) and 12/13 € (100W) either you by in the shop or from the mail (I just asked the price in the shop).
I just add a link to a nice picture that could very well be a power resistor L-Pad mounted on a heatsink (for Wayne -- I know he doesn't want any more heat inside his speakers).
(http://passives.tycoelectronics.com/images/source/Heatsinkassemblies.jpg)