I thought long and hard about getting a 40D over a 30D, but IMO it's just not worth double the price. The 30D has the EXACT same layout as my 5D, and it'll be a backup so I don't expect to use it too often.
I've used a 30D and currently have a 40D, and I can say the 40D is quite a bigger jump from the 30D than the 30D was from the 20D.
Improvements:
2 more MP
Better AF: all 9 are cross points, center point extra sensitive at f/2.8
Faster: 6.5 FPS vs 5, much bigger shooting buffer
Live View (this is actually very useful in some cases, for example when you want to shoot at ground level but do not want to lie on your stomach)
14-bit RAW files have a bit more headroom in PP
Built in sensor cleaning
Bigger viewfinder
Bigger LCD (more accurate colors too)
ISO in viewfinder
Camera doesn't turn off if you open the CF door
3 Custom modes (5D only has 1)
On POTN, I see used 40D bodies with <5k clicks for only around $575-650, while 30D bodies are going for around $400-450 at the moment. Certainly not twice the price for a 40D, and I feel that the improvements are much more than minor ones. If anything, I feel that the jump from 30D to 40D is much bigger than the jump from either 20D->30D or from 40D->50D.
I'm also considering a Tokina 11-16 or Tokina 10-17 fisheye for my new wide lens. I used to have a 10-17 at one point and loved it. It'd be great to have a fisheye that could work on both of my cameras.
Do you really use fisheyes enough to warrant spending $5-600 for one over a wide-angle? IMO a ultrawide is much more useful for most things. Also, you don't really need to spend ~$600 for an autofocus fisheye, since with a fisheye you hardly ever need to focus (due to huge DoF). I do gigapixel panorama photography with a fisheye, and the lens we're using right now is a Saymang 8mm f/3.5 Aspherical fisheye. It has pretty good image quality even wide open and is much cheaper than the Canon 15mm fisheye or Tokina 10-17mm.
You can find re-branded versions of the Samyang marketed as the Opteka 6.5m or Vivitar 7mm. All are the same lens (the focal length difference is due to the different projection used to calculate FL), and some variants are only around $250.
Here's a little more info on it:
http://photorumors.com/2009/05/04/samyang-8-mm-f35-aspherical-if-mc-fish-eye-for-nikon/