Welcome to the iPad club!
If you Facebook, do check out Friendly--there's no official FB app and this one works well (when it does work, due to FB's constantly changing code I think).
You must try Flipboard. It's a great-looking way to explore your most-visited websites; better still if those websites are picture intensive.
For paid apps, I'm happy with the cash I forked out for:
ComicZeal
Reeder (RSS reader)
As for accessories:
Consider the Camera Connection Kit. It's got some usefulness with DACs, as has been discussed here on Head-Fi, but it's also convenient if you're going to be out and about with a camera. The Kit comes w a USB dock adaptor, and a SD card reading dock adaptor--the latter is really, really useful. No more carting around extra wires! Even works with RAW images off a DSLR.
For a case, try looking out for folio-style cases. They often fold to support the iPad in landscape (and sometimes portrait) orientation at multiple heights, which is great when you want to watch movies. They also protect both front and back.
At the very least, you'll want a sleeve (e.g. http://www.macworld.com/reviews/collection/3907/ipadsleevereviews.html) to keep the device slim, but protected against scratches.
