I have a reprint of the 1911 Roget’s International Thesaurus. When I am really stumped, that book is invaluable; yet, although I have this volume by my bed, I invariablly use the following online thesaurus: http://www.thesaurus.com/
[A thesaurus provides words that mean essentially the same thing. This helps prevent the same word too many times].
If you click on the word Dictionary [to the left of where it says Thesaurus], you will have an online dictionary. http://dictionary.reference.com/
I keep those links always open on my computer.
I also keep rhyme.com open.
If you’re writing assonance, you’ll find a chart of similar vowel sounds here: http://www.yourdictionary.com/index.php/pdf/articles/163.longvowelwordsexamples.pdf
Today, I wanted to do some alliteration [writing with words that start with the same letter].
Here is a place for finding nouns beginning with the letter you want: http://nounsstarting.com/
I needed a verb that begins with S. I went to Google and searched for a list of words beginning with S, and found the greatest resource–my newest best friend. You can click on the following and scroll down a bit. You will see that you can find verbs beginning with any letter: http://www.easypacelearning.com/english-books/verbs-a-to-z-list-learning-english/460-s-verbs-list-learning-english-verbs