Right now I'm looking at the Kindle DX and the iPad. Honestly, for technical material I really like the iPad, but it is crazy expensive. I was hoping I could get some views from others or, better yet, reviews on their own purchase, whether it be one of these or another product. Like I mentioned, my greatest need is for reading programming books.

Kindle DX
-Pros
Best selection of books (programming, technical)
e-Ink
Free 3G/Whispernet

-Cons
Black and white display
Next page button only on one side (even more awkward when rotated to landscape)
Proprietary format books
Functionality limited to ebooks and simple web browsing

iPad
-Pros
COLOR
Wide range of functionality
Can purchase/view Kindle books using Kindle reader app
Compatible with more ebook formats
Much more intuitive interface

-Cons
PRICE (it's almost stupidly expensive)
No USB port (which would be more useful on a device with this much functionality)
Somehow, some way, I'm bound to get screwed over by Apple including some must-have feature in the next version for which there is no reasonable justification for its absence on this one.

have you considered other less expensive slates?

http://portables.about.com/od/otherdevices/tp/Slate_tablet_roundup.htm

I know the new kindles just had a huge price drop, and other companies are expected to match the prices by this holiday (might be worth waiting).

I wouldn't get an ipad in it's current iteration if I wasn't doing any development on it, but that's mostly just because I personally have no need for it, which is probably different for you.

quick edit:
One thing that might be overlooked is I'm fairly certain actual e-readers rather than slates have tremendous battery life because of their screen technology. With their wireless off the smaller ones can last up to a month, and with it on they last a week to three weeks depending on the version. Way better than the 6-10 hours you'd get with an ipad or slate.

I haven't looked at the newest Kindle, but I love my first-gen one (and got my mother a second-gen one for Christmas last year which was pretty slick).

I had an iPad and returned it. I won't buy another one unless I need to develop on it or until the second generation comes out (and even then, only maybe).

That's really all I can tell you.

I have the Kindle DX 2 and I love it. If you plan to read PDFs on an e-ink display, this is the way to go. I mainly use it to read journal articles, so I don't have much experience buying books or browsing on it.

My main workstation is Linux-based, so it's wonderful that I can just plug it in via a standard cable and drop files on (i.e. no ridiculous iTunes). No support for epub, but there are workarounds.

Lastly, battery life has been way beyond what I expected. I used it the entire summer without another charge, reading a few hours every day. I'd like to see an iPad do that! Keep in mind, however, that I've had the wireless off all this time.

I personally own a Nook and love it, except it does freeze up occasionally. I know a guy with the Kindle and if I need to get another e-book, I'd buy it over the iPad hands down.

I prefer the Nook because you can load your own PDFs/Documents in a variety of formats, including ePubs. I would shy away from the iPad just as a book reader. That's my 2 cents worth.