If you don’t already have something like a brick in there, you could fill them with water and put them in your toilet cistern. I realise that’s only a one (or two) off thing though - but at least it’s a start!

Sometimes you get down to either start making your own (Better Basics for the Home has good recipes) or just recycling the bottles. There may be a few applications for these, but not as many projects as you are going to generate bottles.

You can cut off the top and screw them onto your bike as bottle holders, though. Or cut them in half lengthwise for DIY-looking bike fenders.

Cut off the bottom and punch holes all over. Push into soil and fill with water.

I’ve not tried it, but apparently you can do without shampoo. You do something with baking soda and apple cider vinegar instead. Google “go no poo” for more information.

I posted a blurb on my blog about Rebecca Crawford (Spacefruit)who collected shampoo bottles washed up on her beach and made great necklaces out of them. The photo of one of her creations is posted. It’s really a great idea.
http://vertes-et-mures.blogspot.com/2007/07/des-dchets-pour-des-bijoux.html

Shampoo bottles can make absolutely lovely bracelets/necklaces. Just Cut circles out of them, put a hole in the middle and thread them onto string! Obviously looks better with coloured shampoo bottles but clear ones can still be used.

make a string and plastic curtain out of cut out bits and pieces.

if you are into scrap-booking you can use them to make the diecut shapes.

I use them as part of pendants, action figure accesories (makes great wings and capes)

Remove the cover and the labels, cut the screw top, put something heavy inside and use it as a vase. Same can be used for a desktop pencil/pen organizer (use other cut shampoo bottles to divide into sections).

i solved this problem for myself by buying solid shampoo. i’m totally against liquid washing detergent and always buy powder (as basically, liquid detergent is just the poweder mixed with water. so we’re paying for water to be trasported etc! madness) sam goes for shampoo. buy solid shampoo bars, most have no packaging whatsoever, and any that do, it will be recycled and recyclable again. it’s soo silly to pay for water when you can just buy the concentrated item, and NO packaging either! solved!

try http://www.lush.co.uk/categories/Bars_72.aspx

or make your own:
http://www.thesoapkitchen.co.uk/solid_shampoo_recipe.htm

Buy in bulk! Refill the bottle with a new shampoo.

Or, like glitterpixie said, use Lush’s bar soap! it totally kicks ass, especially if you travel.

Also, it’s true. You don’t really need to shampoo that often.

Big round bottles can be made pots for plants.
Small hotel size bottles are best kept, at least the pretty ones. Then just refill from the bigger ones.