The tools are available for "free" but I'd strongly suggest anyone who's interested in toying around with them to pay the $400 and get the Select membership (or the $99 Student membership if eligible).
$400 is a lot of money for someone like me who doesn't write Apple software for a living. Nonetheless I am very interested in Apple software and seeing just what I can do with it as a hobbyist.
They send you lots of software. In the month I've been a member I've received 16 CD-ROMs of stuff (This will undoubtedly go down possibly to one a month) and I get access to the online seeding site where the latest and greatest pre-release software is posted. I'm under a strict non-disclosure agreement so I won't say anything more, but if you're a reader of the Mac rumors sites... Forget them. You'll be allowed full and legal access to much of the software they tout as "exclusive sneak previews". Even better you'll have it faster and with a full version to test on your own hardware rather than rely on their poor reviews to set your expectations about what's coming from Cupertino.
Besides software though, the big deal about a paid membership was access to the Developer TV Quicktime movies. Apple offers Quicktime movies of many of the sessions at the WorldWide Developer Conference from this year. They are fantastic introductions to everything specifically Macintosh. What's there to know? A LOT! This is absolutely an indispensible tool to attack the steep learning curve to learn about what it is to program a Mac (be it in Carbon, Cocoa, or whatever).
I'm not a shill trying to sell this stuff to anyone. I just want to say that I have zero reservations about having spent so much money for a paid membership and I'd strongly encourage others to look into it. Even at $400 it's a real bargain.