In Japan, Puffy have had a handful of books published about them, and have even had their own storybook published. Most of the books referenced were published within the first three years of Puffy's existence, when they were very heavily promoted and had their own TV show - no fewer than three books were published in conjunction with Pa-Pa-Pa-Pa-Puffy.
Note that this list doesn't contain any of the scores of magazines Puffy have been featured in over the years, nor does it contain anything published here in the States - it's probably not even near close to listing all of the official books that have been published about Puffy, even in Japan. In the U.S., any and all reading material related to Puffy (except magazine articles and stuff like that) is tied in with Hi Hi Puffy AmiYumi - activity books, children's novels, sticker books, and the like.
Run! Puffy! Run! - February 28, 1997
Boon! Puffy! Boon! (Photo Magazine) - August 12, 1997
Pa-Pa-Pa-Pa-Puffy - June 30, 1998
Pa-Pa-Pa-Pa-Puffy 2 - December 19, 1998
PUFFY Daikichi Vol. 1 - August 15, 1999
Pa-Pa-Pa-Pa-Puffy 3 - October 7, 1999
Sore wa Nanika to Tazunetara - July 5, 2000
Smile (Original Storybook by Puffy) - December 1, 2002
Hi Hi Puffy ENGLISH - February 18, 2006
Ayumi - PUFFY 10th Anniversary Book - March 24, 2006
TSUKI ICHI - December 4, 2008
CD-ROMs & Video Games
Surprisingly, Puffy have had more English-language video games released than Japan-exclusive ones. Not surprisingly, both English-language games were tie-ins with Hi Hi Puffy AmiYumi. Having never played any of Puffy's video games, I can't vouch for their quality. Also, Puffy had a special CD-ROM release in Japan back in 1997. I've never seen that, either.
Supposedly there was supposed to be another game based on Hi Hi Puffy AmiYumi - for the Nintendo Gamecube - released in late 2006, but to my knowledge nothing ever came of it.
For images (and some more info) on some of the books and games listed above, click here.
Wallpapers & Other Stuff
Wallpapers and Other stuff. Pretty self-explanatory.
More to Come! ...Maybe.