There's another use for a Book Of Exalted Deeds, and that's as fuel for a campaign with evil PCs. Some may frown upon this, but they're out there. As it currently stands, there are far too few 'good' opponents for such people. Sure, you've got elves... and humans, and dwarves, and lammasu, and a couple of others, but really, where are the goody-two-shoes to smack around?
Of course, I don't necessarily condone this... it simply appears to be a gap in the material available.
The idea of the BoED is interesting, however, and not just because of the aforementioned perspective. So long as it's done well, that is. Keep it flexible and open and put the emphasis on enriching options, not preaching or putting up restrictions.
I'd like to see more kinds of celestials (how many kinds of demons/devils/yugoloths are there by now?), more good creatures of a more mundane nature, and of course some guidelines as to what goodness is, but not restrictive ones. (I firmly believe in the sandbox approach to gaming; that is, give as little as possible and let people play with it.) An interesting idea might be a virtue system like old Ultima games had... you know, where you got rated in various attributes like valour, charity, mercy etc. Although what you'd use it for is an interesting question...
Now as to the person who mentioned Aztecs and Romans... we don't always think of them as evil, although they did some pretty abhorrent things. But think about it. In one thousand years, who will people remember from the 20th century? Probably Hitler. Only obscure scholars will have ever heard of Churchill or Roosevelt or whoever they were. (See, it's already starting to fade.) The Aztecs and Romans are remembered for exactly the same reasons: They conquered very very well. Of course, they're not here today. Were they evil? To some, certainly. It takes a certain mentality to put your own people above others then go out and conquer them. Just thought I'd mention it.
And as for books on Order and Chaos, those could actually be far more interesting because they have much less moral background. Law and chaos are opposites, and neither one is 'right' as you might describe Good. A good deal of fantasy literature deals with describing the struggle between gods of Chaos and Order.
Now whoever it was who said that a book of Law would be boring? I don't think so. Part of order is building things up. Mundane examples of Law include: How to put a legion together; How to build a monolithic monument akin to the Pyramids; How to write a set of laws that cover all the bases. Now I happen to think that writing my own laws would be pretty cool, especially if I had subjects to obey them. Then you go into extraplanar Law; there are some cool metaphysical concepts you could visit there. Crystal, for example, is a very lawful material in my mind; imagine an entire plane made of crystal, walking though a shining forest or fighting a crystal template lion that shatters easily but does more damage. The coolest thing about Law, however, is that the Borg are lawful (either LN or LE, it's difficult to decide). Seeing Borg-like foes in D&D could definitely be exciting.
Anyways, those are just my thoughts on the matter. I'm poor and probably won't buy anything mentioned here. I just think it's a cool idea.