There's a two page report on toothpaste and whitening claims in
August's Consumer Reports (Pg. 12).

Forty-one toothpastes were rated for stain-removal and categorized
based on: abrasiveness, tartar control claim, plaque control claim,
unusual burning taste, unusual bitter taste, and unusual mouthwash
taste. (I'm guessing the "burning" is more of a sensation.)

Toothpastes that contain "less fluoride than others" (but remain within
ADA's accepted range) and toothpastes that contain no fluoride are
indicated as such.

One toothpaste ranked "excellent", twelve ranked "very good", twenty
three ranked "good", and five ranked "fair".

The brands rated are: Aim, Aquafresh, Arm & Hammer, Colgate, Crest,
Listerine, Mentadent, The Natural Dentist, Rembrandt, Sensodyne, Tom's
of Maine, Ultrabright.

The "price per ounce" of the toothpastes ranged from $.28 for
Ultrabright All in One Advanced Whitening to $2.73 for Rembrandt Plus
Premium Whitening.

Stain-removal effectiveness isn't dependent on price.

The report also includes some definitions of toothpaste terms.

(Hint: $.28 per/oz will buy you the best ... with average abrasiveness.)