If you have Frostburn, you might check out the Primeval.
for ex
Neanderthal Barbarian8/ Primeval10/ Warshaper 2
I like DireApe (Rend, yay!) as the Primeval form, but if you want a bear shape then ask if you can use the Polar Bear since the Dire Bear has too many HD (could be a 8hd Dire Bear).
Endurance, Self Sufficient and (improved) Toughness are required, but that leads into Steadfast Determination, leaving 3 open feats. Animal Devotion (CChamp) gets you a +8 str boost, or other maybe useful animal power (Flight!), and without magic it might be quite handy, so you could take it 3 times.
Assuming a starting str of 18 +2 race, + 4 levels, +3 regression, +4 rage*, + 8 Sacred*, +16[22] Primeval Form** (Polar Bear) [+6 Feral Power] nets a 61str (+25) @ 18th w/o magic (62 @ 20th).
Con gets up to (assuming) 16+2 race + 4 rage* , +3 regression, + 8[12] Primeval form** [+4 Feral Power] for a 37 (+13).
* 3/day each
** 4/day
Attacks (w/o magic)
+43 Claw d8+25
+43 Claw d8+25
+38 Bite 2d6+12
Improved Grapple +51
+13 Natural Armor in bear form
Primeval 10 grants [shapechanger], Dr10/magic, and you count as a Magical Beast instead of a Humanoid
Warshaper 1 @ 19th gets you Improved Natural attack
Warshaper 2 @ 20th gets you an extra +4 str/con when in Primeval form, and the 5th ability improvement point.
Other Forms:
Dire Lion loses 2 str and 2 con, but picks up the extra rake attacks and pounce
I like the Dire Ape since it retains a (vaguely) humanoid form, and if you hit with both claw attacks you rend for double claw damage extra, dealing up to 4x claw damage total.
