MOTM

I'm starting to try and locate all the parts to start making some kits
for myself with the bare boards.  One piece I'm not too sure about is
the Ferrite Beads... is there any particular
resistance/tolerance/impedance/heat tolerance that I need to look for?
Any particular shops to buy from?  I've found most everything else at
Mouser and I'm trying to get as much from them as I can so as to
hopefully just have to pay one shipping charge...
thanks,
Ti_