I've found that a Nissan stainless bottle works very well, keeping liquid cold up to a couple of hours during summer rides. Easy to clean, very durable, and better cooling than the insulated plastic variety. Steel is obviously heavier than plastic, but I'm not a good enough rider to be able to notice an impact. I've not been concerned on organized rides or in open country about anybody taking it; in other circumstances (e.g. lakefront bike path) I just take it with me and refill before resuming the ride. To avoid metal/metal knocking, I put a polypro jacket around it (also lessens cold loss), but a carbon bottle holder would probably work also.