Variations on a palindrome (in order of increasing length):
A man, a plan, a canal, Panama!. A man, a plan, a cat, a canal; Panama? (by Jim Saxe). A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal--Panama! (by Guy Jacobson). Panama, 49-word version (by Guy Steele). Panama, 102-word doubled version (by Ford Prefect?). Panama, 543-word version (by Dan Hoey). Panama, 988-word version. A dog, a plan, a canal: pagoda.. A fake Panama (not a palindrome).
Variations on a different palindrome...
Enid and Edna dine. Enid and Dena dine. (not a palindrome). Dennis and Edna sinned.. Dennis and Edna, 63-word version. fake Dennis and Edna (not a palindrome).
Palindromes based on words rather than on individual letters:
So patient a doctor, to try to doctor a patient so. You can cage a swallow, can't you, but you can't swallow a cage, can you? Girl, bathing on Bikini, eyeing boy, finds boy eyeing bikini on bathing girl. Amusing is: that company of fond people bores people fond of company that is amusing.
Finally, a couple of poems whose lines form palindromes.
If you really like palindromes, there are many collections on the Wibbly
Wobbly Web. Here is one:
Jim Kalb's Palindrome Collection.