The next big update to Mac OS X gets a release date, along with a ridiculously low price: just $29. Meanwhile, both the 15-inch and 13-inch MacBook Pros (that’s right, 13-inch MacBook Pro) get SD card slots, better battery life, and price drops.First, let’s cover Mac OS X 10.6, a.k.a. “Snow Leopard,” the big under-the-hood maintenance update that finally got a release date (or month, anyway) during Monday’s Worldwide Developers Conference: September, as expected. And the price? Just $29, or $49 for the multi-license “family pack,” far less than many (including me) had expected. [Update: Keep in mind that the $29 upgrade price is for 10.5 “Leopard” users only; if you’re still using 10.4 “Tiger,” you’ll have to pony up $169 for a combo pack, which includes iLife ‘09.

Apple execs ticked off several of the new features in Snow Leopard (most of which we’ve seen before), including a slimmed-down QuickTime player (now called QuickTime X), support for Exchange servers, improved overall performance (courtesy of a “set of technologies” called “Grand Central”), and a rewritten Finder. Also nice: Snow Leopard only has half the installation “footprint” of Mac OS X 10.5 “Leopard,” and should “recover” several gigs of hard drive space once installed, Apple claims.

Meanwhile, we also got a series of MacBook Pro announcements, including word that both the 15-inch MacBook Pro and 13-inch MacBook (now promoted to “Pro” status, incidentally) are getting the same built-in, non-removable battery that’s currently in the 17-inch MacBook Pro (which gets a $300 price drop today).

Apple promises a good seven hours of battery life from the “revolutionary” lithium polymer battery, which it claims will last for five years without any degradation in performance.

Also new: A built-in SD memory card slot for the 15-inch and 13-inch laptops. SD memory cards are incredibly common—indeed, if you’ve got a digital camera, it probably uses SD memory—and the addition of SD slots to the MacBook Pro line (they’ll be replacing the little-used ExpressCard ports) is long overdue. Both models will also get FireWire 800 ports.

Other new features: Upgraded, more vivid LCD displays (making for “the nicest display we’ve ever had in a notebook,” according to Apple SVP Phi Schiller), as well as mammoth hard drives—500GB, or a 256GB solid-state drive—and bumped up processor speeds (up to 3GHz for the 15-inch MacBook Pro) as memory capacities (up to 8GB of RAM).

Shipping now, the new, entry-level 15-inch MacBook Pro (with a 2.53Gz processor, 4GB of DD2 RAM, a 250GB hard drive, and discrete NVidia 9400M graphics) goes for $1699—a $300 price drop compared to the previous model—while the cheapest new 13-inch MacBook Pro will sell for $1199 (2.26GHz processor, 2GB of RAM, 160GB hard drive, and the NVidia 9400M graphics card).

Meanwhile, Apple’s thin-and-light MacBook Air got a serious price drop: Just $1,799 for a 2.13GHz Air with 2GB of RAM and a 128GB solid-state hard drive, $700 cheaper than before, while the entry-level air now goes for $1,499 (1.86GHz, 2GB RAM, 120GB hard drive).