In reply to StuM: I tote 2 bodies, 3 lenses, flash, flash bracket, 1.4 converter, plus loads of bits n bobs.
Lowe Pro Mini Trekker AW for most of the time, but I have a second hand Billingham 335 shoulder bag for 'quick access' days.
Both are perfect for what I use them for.
Neither is THE perfect bag, but then nothing is...
Best thing is to put your kit into various ones, to see what fits. Bear in mind, you might just buy a 2nd body, more lenses, a bigger flash, etc. So allow room to grow.
TTG