Adobe Riskbreaker pointed out in a post on the forum at Halo.bungie.org that EBWorld now has an entry for Halo.

In addition to listing the (what must be speculative) release date of January 30, 2001, it also cites a price of $49.99, and has two short reviews from material presented at E3 as well as last year's MacWorld New York. There is also a page of customer reviews. There are several of the latter already there, running the gamut from amazing to kick ass .

Interestingly, the main Halo page at EBWorld mentions the following:

EBWorld.com customers who bought this item also bought:

Diablo II	PC $49.99
B-17 Flying Fortress	PC $44.99
F/A-18	PC $37.99
Starlancer	PC $39.99

I'm not sure how this is possible if no one has actually bought Halo yet, but I suppose some adventurous souls might have put in for a pre-order. But if you're going to do that, you might as well wait and pre-order from the Bungie Store when they make that option available.