I decided to start this guide, because of PinkShinigami´s request of a complete guide.
I think together we can get a pretty good and complete guide^^
~Albums~
A Best
1st press comes with a slipcase and 6 different Covers inside
Slipcase:

Covers:
Normal Edition has the Slipcase Picture as Cover
I am...
1st Press has an extra long Obi that covers the whole back of the CD case
Rainbow
1st press had a code to download Track 00 (Rainbow 44sec instrumantal)
I also heard that it came with a mini a shaped calendar (at least my OV had one)
*pic of calendar will be added soon*
A Ballads
1st Press came with a slipcase and 4 different covers inside.
Also I have heard there was a very limited pressing with black disc (that´s why OV is black, OVs often have JV 1st press bonus as regual edition)
Slipcase:

Covers:
Regular Edition has the slipcase picture as Cover
My Story
The CD+DVD 1st press came with 4 different Covers. Regual press has same cover as CD Only.
The earlier 1st presses also came with an error booklet as they made a mistake.
1st press:

Regular:
Error Booklet
http://eneabba.net/ayu/disco/albums/...ORY-4a.all.jpg
(miss)understood
1st press of CD+DVD came with the photobook "on my way". 1st press of CD only came with photobook "off my day".
CD+DVD + on my way:

CD Only + off my day:
Secret
1st press comes with a (textless) Poster
A Best 2 Black & White
All Editions of A Best 2 1st press came with black/white colored case. CD+DVD also had a slipcase.
Early 1st press also have a Error Booklet because they made a mistake
1st Press examples (2nd pic shows the error booklet that was put in front of cover):

Regular examples:

Guilty
1st press of CD+DVD and CD Only came with a Photobook.
A Complete
1st press of 3CD+DVD Version comes with a 48p Photobook and a Box.
1st press:

Regular:
Picture Credits: eneabba.net + YJA