O_o This forum...it's ali~ive! Stopped by here on a whim, but since I'm bored, here's a list of the JK merch that I know of (*'d ones I own, so I can answer specific questions about those, but please don't ask for scans of everything, as I haven't the patience to do that and besides, who knows if I'll stop by here again?

).
* trading cards (full set = 99 cards)
* shitajiki (pencil boards)
---> 3 styles of "clear" shitajiki:
*1,
2
---> *2 regular shitajiki drawn anime style
*
clear posters x3
- regular posters (links to actual DVDs, but pic's the same as the respective covers)
---> *anime collage (Youko centered; with Rakushun, Shouryuu, Enki, Keiki in background)
---> *DVD promo
1 (*sigh* I'd have gotten this signed by Hisakawa "Youko" Aya if I'd known she was going to be at Animazement this year ;_; )
---> DVD promo
2
---> *DVD promo
3 (mine's signed by JK director Kobayashi Tsuneo

)
---> *game 1 promo (anime style Youko in armor, facing front w/ an unsheathed Suiguutou)
---> *game 2
promo (has at least 1-2 variations with more writing covering the pic)
-
postcard sets x2 (6 postcards per set)
- telephone cards x2:
1,
2
-
bookmark sets x2 (6 bookmarks per set)
- give-away goods (i.e. promo stuff not to be found in stores

)
---> Rakushun cellphone strap (pictured
here)
---> Rakushun monitor cleaner (?) - it looks like a Beanie Baby-ish Rakushun plush whose belly is used to clean your monitor display (haha)
-
mousepad
-
memo paper
-
"post card file" (? - not sure what this is for)
* Studio Pierrot 25th Anniversary
repro autograph card (it's a little smaller than the standard shikishi, or autograph card)
Others have already mentioned the calendars, CDs, DVDs, novels, anime comics, and the anime guide book. There might be other DVD promo posters, but those above are the only ones I've seen so far. I've gotten most of my posters at cons. Other books not yet mentioned by other posters include the 5 anime script collections (interesting for the scriptwriter's behind-the-scenes remarks/footnotes) and 2 (I think, as I only have 1 of them) sheet music collections (easy-intermediate piano arrangements).