Barbarian 20/Fighter 10 works...
Barbarian 20/Divine Champion 10 works...
Barbarian 20/Dragonwarrior 10 works...
Barbarian 20/Dragon Slayer 10 works...
Barbarian 20/Etc...
Northlander Hewing is lovely feat to have on a high strength barbarian. Not sure about one hander though.
As for Barbarian 20/Frenzied Berserker 10... I think that is a bit of a 'meh' choice to be honest. It would be different if Epic Rage and Frenzy stacked properly to +20 Strength, which they do not, so you get +12 at most. Thus you might just go for Epic Strength for +10 and use any +2 Strength item to get full +12.
Now, if you skip Northlander Hewing, Barbarian 21/Frenzied Berserker 5/Fighter 4 works quite well too.
Anyhow, your best multiclassing choices are Divine Champion and Fighter simply because of the bonus feats that the two grant. (Those bonus feats when taken during epic levels can be spent on Epic Damage Reduction, Epic Toughness, Epic Prowess, and few more feats.)
Thus... basically, just max out your strength and get something like 21 in constitution for the Epic Damage Reduction feats. The "14/-" you get this way is nothing to shrug at against the regular mobs.
Moreover, Divine Champion is the better choice because it will also improve your saves. (You can make your character a divine champion of a 'Frenzied Berserker' deity, and you got the 'FB RP' going for you as well.)
