If you have kids, you probably have a heightened awareness of BPA. Bisphenol A is found in plastics (of most concern, sippy cups and bottles). It has been linked to everything from breast and testicular cancer to genetic abnormalities to obesity. It also does nasty stuff to marine life. You can recognize a BPA plastic by the recycle symbol on the bottom. If it is a 7 or a 3 -- it can leach BPA.
I have been wanting to switch over to a environmentally friendly water bottle for each of our family members and I was about to buy the aluminum Sigg (even though I was wary of aluminum due to its own health risks) when Sigg came out with a big "whoopsie" about their liners having BPA in them.
So stainless steel it is!
Klean Kanteen is the leader in stainless steel water bottles. My REI fans in the NW are long aware of the Klean Kanteen, standards for the hiking and camping crowd. Easy to clean.
I want to get a set of 12oz (powder coated) w. the poly sport cap for my kids. Same thing in a 27 oz for the hubby and I.
The Soft Landing is a great site that specializes in low-impact / nontoxic solutions. They have the stainless steel food thermos that will be great in Miss Crab's lunchbox this winter.