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The greatest clown book is a trilogy by Bruce "Charlie" Johnson.
www.charliethejugglingclown.com/

It is called Creativity for Entertainers. There are three books and
they range from how and where creativity originates in your brain to actual routines
and how to tweak them to fit your clown character.

The second book is my favorite and it lists different stimuli to monkey wrench originality
from life and mental ether. And use it to construct skits, character elements and black outs
walk arounds etc etc.

here is an example;

Joks whacks to the head (Book 2 pg 179)
(write these on scraps of paper and throw them in your hat, pick one out when you reach a creative block)

1.) Listen to the quiet voice inside
2.) Reverse the order of your jobs
3.) make the mistakes more important
4.) If you cant hide something, decorate it
5.) Find the part you like the most
6.)Pay attention to what you really want this line to say
7.) what would a baby do?
8.) I know it is too much, but is it enough?
9.) would your best friend do it another way?
10.) Make a list of the things left to do, and do the last thing on the list.
11.) Does it have more than one way to look?
12.) Trust the artist in you right now
13.) When you have an either or choice, do both.
14.) You have good ideas, really.
15.) Do the thing that is impossible.
16.) Take a nice break . Refresh.
17.) Accept some advice, dont question it.
18.) Do the exact opposite of the advice
19.) does your body have a physical feeling right now? What does it say to you?
20.) Use a color that noone in his right mind would use.
21.) Plow right ahead.

then Charlie adds a few, some from Jok some of his own.

22.) close eyes, open the yellow pages, point to somewhere on that page. Open eyes, that is the germ of your project, like it or not.
23.) Remember to accerorize! A Lot! Our ability to accerorize separates us from the animals.
24.) If it isnt Fun, make it fun. Stop going for the laugh, just make it fun! Only you know how to do that.
25.) Break a rule
26.) Cut it in half
27.) Do it silently
28.) Make it rhyme
29.) Do it backwards, or otherwise change the order.
30.) End with the beginning, what came before this?
31.) Switch Roles
32.) Eliminate a character
33.) Add another character
34.) Go as Slow as Possible
35.) Go as Fast as possible
36.) Use a series of poses like comic strip panels
37.) Do it without props.
38.) Transform your props into something else.
39.) Stop to read a book unrelated to entertainment.
40.) Do something physical
41.) Ask a lay person.
42.) How would your favorite comedian do it (how would Britney/ george bush do it?)
43.) Listen to music
44.) How would it be done in an animated cartoon? (In anime, a hong kong mrtial arts movie, Bollywood musical...)
45.) Turn it over
46.) Do it on the other side.
47.) Why?
48.) Begin at the end, what comes after this?
49.) Change the name
50.) Take a humor break
51.) Combine with another idea.
52.) Ask another entertainer

Wow, what an incredible list! The favorites link you posted didn't work, but clownbooks.com did and it's amazing. Thank you so much for putting this together, it's an invaluable resource indeed.