Hmm well where do I start... I have been aggresivly collecting obscure Dreamcast discs under the 610 catalog id for about a year now. I have also been cataloging them and saving any image records I can find.
So far I know of 167 known releases with a 610-XXXX catalog id. The list is still growing. I actually own over 88 of these myself, and I have images of roughly 135 of them.
What makes these discs so cool is that, unlike other consoles at the time, the Dreamcast had a proprietary disc format. I find it more interesting collecting demos that are GD-Roms than PS1 or PS2 demos. Also, many of the discs have very interesting goodies on them like the Seventh Cross Fighting Itegration or VOOT 5.66 software on the Official Dreamcast Magazine discs. On one of the Dream Express discs there is virtual tour of TGS where you can walk up to kiosks an then either play the demo of that game or watch a clip. There is this really cool sequence where they video tape you walking in to sit down for the premiere of the D2 trailer in a theatre. From a research and documentation perspective, this disc is critical (I can't remember which volume has this, will have to look it up).
The presentation of the promo discs is pretty unique as well. Some come with a front insert, some with a back insert, some with both, and some with no insert at all. Some have a super plain silkscreen like Get Bass which only has the logo. Where-as Power Stone 2 and Giga Wing have full dual color silk screens covering the entire disc. Some like the Netto de Golf and Super Runabout demos came in bizarre packaging. Netto de Golf comes in this cardboard sleeve with a picture of a big hand with its thumb sticking out with a driver head attached to the thumb. Then the Super Runabout demo is in some sort of necklace thing, in a plastic sleeve.
Some of the rarest promo items that I know of are the Dream Preview discs. If you have a complete set of these consider yourself lucky. I am not talking about the Dream Express discs which are much more common. The Dream Preview discs have a sort of generic looking grayish cover style with loads of text on them.
The rarest item I own, I don't even think the Dreamcast Community is aware of. I would go so far to call it a one of a kind, but maybe someone else has actually run into one. So here is the story:
I was on ebay, when I spoted something I had never seen before "What is that!?" The seller had the most bizarre disc. It was the HITACHI SH-4 Demo Disc. I contacted the seller, threw out an offer, and snagged the item out of the auction individually. It was crammed into a junky import bundle. The most interesting part is that I was able to buy it from the original owner and get the complete story behind it. The disc was handed out in boardroom meetings to people in the chipset and electronics industry. To get one of these discs you had to be in a meeting with Hitachi, and own an actual Dreamcast console. Then they would hand you one. Instead of handing out Demo boards for testing the capabilities of the processor, they simply passed out this disc instead and let people run a variety of technical tests on the Dreamcast console. It was a very novel solution.
From a rarity perspective HITACHI SH-4 Demo Disc is easily the top item in my Dreamcast collection.
If you guys are interested in my recent haul, you can check out the following auction:
The most prized item here is of course... the Bangai-O Demo disc which I have been seeking out for quite sometime now. Notice the cover is nearly identical to that of the retail release, except for a very thin line of text in the gray area below the artwork. This is the first time I had ever seen it before, and was previously unsure of its true existance in the first place. Though maybe I did come across it in the past but never knew it, since the cover is almost the same as the final retail release.
I guess I will end it here for the moment hehe, as I could easily keep writing. Feel free to leave your thoughts.