Barb is a good one-level dip, so I changed Rage to give out 2 temp hit points/barb level and +2 fort save instead of the standard +2 CON (and after reading this, I think I should throw in +2 rounds of rage). Encourages more barb levels and because of the temp hit points, less dead barbs.
For frenzy, I haven't seen it yet, but I would consider having the extra attack at the barb's level instead of your full BAB. So a barb 1/fighter 19 would have attacks at +20/+15/+10/+5/+1 (-2 to each) when frenzying, while a barb 19/fighter 1 would have frenzy attacks at +20/+19/+15/+10/+5 (-2 to each).