My wife found this thread and suggested I post this information about shampoos that come in bar form. Here's what she came up with:

J.R. Liggett: jrliggett.com
scores 2 on scale of 10 for toxicity per cosmeticsdatabase.com

Burt's Bees rosemary-mint solid shampoo bar
scores 1 or 2 on same scale

Burt's Bees baby bee solid shampoo bar
scores 4 on same scale (comparable to liquid shampoos such as Head & Shoulders, Dove grapefruit)--as is not uncommon, the ingredients in the "baby" versions of cosmetics can score worse than the adult variety

Lush: lush.com
scores 4 on same scale (comparable to liquid shampoos such as Head & Shoulders, Dove grapefruit). Because it has SLS in it, it lathers up very nicely. More expensive than the others. They say you can get 80 washes per bar; but not sure how that compares to the # of washes in the others. Lots of varieties for different types of hair, various scents.

Solid shampoo lasts longer if you let it dry after washing and keep it in a closed container.