The original DnD logo is very iconic, simple and probably something to work from. It uses a basic fantasy font in red with a gold outline and rugged textures overlayed on top.
It seems Aaron has already created his own logo for DnDi, you can see it here:
Wether or not you use that is up to you and him, but I suggest doing something similar to the second edition logo of DnD
Instead of using red colors though, you could use blue colors with a gold trim.
I like the latter idea though I'd like to work in a philosophy pun or symbol there, the same way they worked in a Dragon.
As to Aaron's, we've always been a bit iffy about using his work. I think back before I was incharge he veto'd it or something but regardless if I were to put it in the old vets would come back just to slap me around a bit for it. And Mr. Diaz would probably arrive with a lawsuit. And other various horrible things.
Anyway! We have a few old Logos that I can post here [gah, I'll get around to it! Leave me alone!] but they're all fairly bland though we do have on that's definitely a front runner, we generally need more art for it as opposed to just fancy font.
Meta, I think you're too hard on yourself about Aaron's response. As long as we were to ask about using the original logo before using it, I'm sure he'd have no problem with it. And if he does, he'll just say no and then we just we use our own custom logo.
Also, as for the four logos posted, I like the first one the best.
I like the last one the best. But in addition I'd love it if we had a textless logo alternative. Something between the die on a column in our favicon and the symbol d20 by Aaron.
My personal favourites are the first two.
I also have my own textless creation which I'll thrown on later.
As for your suggestion, I'd recommend avoiding d20s since we don't use them. I'd sooner have two d6 with an Ankh for a one, Yin Yang for two, Celtic design for the three, Greek Elements for four, Chinese Elements/Pentagram for 5 and I'd need a 6, but yeah.
Hmm, I like that idea. How about that korean block thingie? I don't know what it's called. It's on the far right on Aaron's d20.
Oh, wait here's an idea - 1-4 as you said, 5 is the korean thingie (split line, full line, split line) and the jewish star for 6.
My wiki has a pretty cool logo - an unidentified person standing on an open book http://editthis.info/wiki42/
maybe some d6 on an open philosophy book might be an idea along the lines of a "textless logo"
Old one, probably not logo worthy, but amusing none the less: