Do white strips work?

White strips actually work, but work best on those with straight teeth and a relatively narrow smile.  They tend to be only six to eight teeth wide, so Julia Roberts-type smiles should look elsewhere.  Because the concentration of the gel can be lower, they may take longer than professional products available through the dentist.  With that said, Procter and Gamble has recently increased the strength on their premium products to levels very close to dental strength products.  No strip, however, can provide the fit, comfort or isolation that a dentist-made custom tray can.  

Do whitening toothpastes, toothbrushes, and mouthwashes work?

Toothbrushes (and toothpastes) that claim to whiten more usually do so by adding extra abrasive.  For people with healthy brushing habits, ADA considers whitening pastes with the ADA seal to be safe for everyday use.  I would specifically avoid the highly abrasive combination of a high speed toothbrush, a brush head with a rubber cup in it, and Ultra-Brite toothpaste.  In extreme cases, you can prematurely wear out your enamel.  Professional tooth whitening is safe, much faster way to whiten most teeth.  Whitening toothpastes may be a good way to minimize the buildup of external stain on teeth between dental visits.

Other products use chemical agents such as hydrogen peroxide.  Hydrogen peroxide, in high strength, will burn gums and soft tissue.  In order to make a product safe for consumer use without dental supervision, over the counter hydrogen peroxide products typically use much a lower strength.  In the case of toothpaste or mouthwash, there usually isn't enough concentration or exposure time in the mouth to make a meaningful difference.