In my humble opinion, I think Canon is still the Queen of point and shoot while Nikon is the King of SLR. There are some cheapish Nikons good for entry level, but the D90 is worth the extra money and is cutting edge for what it offers (HD video, etc.) but you may want to look at spending even a little more for a better lens instead of the one that comes with the kit. Yes, indeed, if you are a beginner it can be intimidating, but they all have full auto functions. And just a bit of reading and experimenting can teach you the basics of f-stop (aperture), ASA, shutter speed, and you can go on from there.
I went on a safari to South Africa two years ago and had the Canon S5 IS, which would be technologically inferior to this camera. I can tell you, though, that the camera worked amazingly well. I got great shots and some good, short movie clips. The zoom was invaluable. Some day I want an SLR but, for now, I like the portability of something smaller so go the point and shoot route. Unless you really want to get into the whole SLR thing (which is really a different niche entirely), you'll be very satisfied with an alternative like this camera. Also, make sure you buy a good pair of binoculars -- Nikon has decent ones that aren't insanely priced. Finally, one last thought about SLRs -- don't let complexity scare you off if you're ready to take the leap, and don't mind the bigger size. I've played around with some, and am certainly no expert, and it's not difficult to take decent shots. Like anything else, though, obviously those with more knowledge, experience, and expertise, take much better than "decent" photos.
Great advice, M. Tobin. I'd like to point out another reason to consider an SLR, though. If you should ever want to shoot through a telescope, you can pop off the lens of the SLR and solidly attach the camera to a telescope with an inexpensive bayonet-ring adapter, widely available through photo shops and online astronomy shops. Why shoot through a telescope? Well, when you find out how beautifully a modern digtital camera captures photons, you just might want more magnification, and much more versatility, than a 12x fixed-lens camera can give you. With a good quality small scope, you can photo an eagle at 300 meters, a lunar eclipse, Jupiter, and so much more. Canon is superior to Nikon for astro photos because of its CMOS chip. Look for a Canon SLR with LCD preview, at least 10MP, preferably (but not necessarily) HD movie mode 30 fps or more, and image stabilization internal to the camera body. With an SLR you also can use specialty lenses such as telephoto and fish-eye. Older Powershots had a removable ring around the lens which allowed direct attachment of camera with lens to a telescope, but Canon seems to have stopped doing this, I don't know why.
Oops, sorry, I messed up two things: no HD movie mode on Canon cameras that I know of.. I meant to recommend a respectable burst-mode rate. The digital Rebel does well, the D40 better. Also, internal image stabi is becoming standard on point-and-shoots like the Powershot, not on SLRs. My bad, sorry for any confusion. Most folks, especially newbies, would be thrilled by the 12.1 MP Canon Rebel's performance, but a D40 with a (spendy) EOS lens is better. The new Nikon 300 might outperform the Canons if you can go to the $1500 price point. For anyone really serious about astro photography with an SLR that also will be an excellent all-round camera, Canon makes a model that has a removable infrared filter... as far as I know, no other brand does this. I have an older 6 MP Rebel with an image-stabi tele lens and it produces stunning images whether in low-light, non-flash situations or snapping wide-sky sunset shots even from a car travelling 50mph on twisty roads.