What are some cool camera lenses?
For a nikon d3100. I would like a fisheye but they're really expensive and I can't find one anywhere for a nikon on ebay or any other sites (if you have any suggestions for those please tell me though!) however, are there any other cool but not too expensive lenses for cameras?
There's an 8mm f3.5 full manual fisheye that's sold under various names for just under $300.
There's holga lenses that can mount on your nikon but, once again, M mode only: http://shop.holgadirect.com/products/holga-nikon-camera-slr-lens-hl-n
And then there's th elensbaby products: http://shop.holgadirect.com/products/holga-nikon-camera-slr-lens-hl-n
The holga and the lensbaby would be considered cool by certain people.
Check out this lens at: http://www.adorama.com/...835NK.html $289.95 with free USA shipping when purchased through the website. Some restrictions apply.
Here is another one: http://www.bhphotovideo.com/...video.com/c/product/769466-REG/Rokinon_FE8M_N_8mm_Ultra_Wide_Angle.html" class='ext_link'>http://www.bhphotovideo.com/...Angle.html
You can check out the Lensbaby line here: http://lensbaby.com
Both Adorama and B&H carry the full Lensbaby line and will likely have very comparable prices.
What does 'cool' mean?
Don't laugh - it is a serious question. I really want to know what you are describing in a camera lense when you call it 'cool'.
Try going to B&H photo they sell everything you could want but more then that they give descriptions of everything and even have user reviews it is a great place to get information. Then if you decide to look for the lenses some where else you will know what it is you want and can make a more educated search. Here is the website hope it helps http://www.bhphotovideo.com/
Take a look at Rokinon FE8M-N 8mm F3.5 Fisheye Lens. It a fairly good and inexpensive lens. I suggest you read this review to aid in your decision:
http://www.amazon.com/...TWIB3PAA9/
This is the best price i could find for it:
http://www.amazon.com/...002LTWDSK/
And i really don't understand what you mean by "cool", so i can't really recommend a lens for "cool" photography.