1. Use a digital camera that has a LCD display so you can scan results immediately ( trial and error is a big component of good digital photography of aquariums) Sometimes I take 5 pictures to get one that I am semi happy with - aquarium photography must be one of the hardest pictures to take, especially close ups of moving fish.

2. Use the flash or don't use the flash - for some reason the colors bleach out and blur on my camera if I don't, but others seem to have the opposite problem. Add extra light temporarily atop your tank for the pictures. An external flash will enable you to take pictures directly without flash back by moving the flash to the side. Not all cameras will accept external flash, only those with the click on flash, will. 

3. Take the picture at a slight angle to the glass to eliminate / minimize "Flash Back" - This is where trial and error take place. Sometimes taking the picture slightly down wards and slightly to the side is the best angle.  Also take pictures at night with all the lights off in your house including the TV. This reduces glare caused by such things.

Note that most good photo software has a "distort" option where you can straighten out a picture taken at a slight angle.

4. A good digital camera that takes screw on filters makes it real nice. I use a polarized lens filter to make the colors look somewhat truer than I would normally attain.

5. Focus - watch your autofcus try to decide whether it should focus on an object or the glass. Glare from daytime, smudge on the outside glass, or algae on the inside glass can really mess with auto focus cameras. If you have a camera that can focus manually, you can learn how to use it. Another key is to take your pictures a little farther away and use photo software to clip out the subject in the middle of the picture. I get some of my clearest closeup pictures by doing this. Use higher speed shutter settings for moving fish. the equivalent of 400 film should work fine. A tripod will greatly increase the clarity of your pictures because you can get rid of the camera movement.

6. Shrink your picture size to 6" by 5" by 150K using photography software like "Adobe Photo Deluxe" and then convert it back into jpg format for universal use. You can also manipulate the brightness and perhaps fix coloration during your stint with the photo software. You can't play with it too much or you will have to start over.

I have an Olympus Camedia C-720 Ultra Zoom Digital camera with an 8 times optical zoom. Digital zooms are worthless in my experience but the optical is great. I am really happy with my camera although I wish it would accept an external flash and it does not 

http://www.geocities.com/NapaValley/5491/photography.html

http://www.characin.com/carey/articles/00/quest-for-digital-images.html

http://members.aol.com/yamatoaquariums/photography.html

Try to remember how you took a shot (may want to even jot down a note). That way when you come across a picture you like you can repeat the technique. The one mode you may want to consider is the slow shutter-low light. I don't like the pictures that I take with the flash. Too stark and the fish looked frightened. The downside to the low light is getting them to stand still <GRIN>. 90% of my shots are blurry due to the fish swimming or turning quickly. I try to anticipate where they are going to move to and lead them as this mode takes about a 1-1/2 seconds to record the shot. I get about one keeper for every eight pictures taken.  I get a lot of blurred pictures and shot of tails.

I use a tripod and that really helps with the clarity. I try to make sure there are no reflections from my PC, TV or lights. I don't like to use a flash either. I use the "twilight" mode (slow shutter). Because of this you really need a tripod or a extremely steady hand. Sometimes the pictures come out on the dark side and I'll lighten them up in Paint Shop Pro. Because of the slow shutter and quick movement comes out blurred. My Parrots are easy to photograph because they hover and stare at the camera.

Sony DSC-P51 (from J&R Music $239 last October)
2 mega pixel
These are settings I found work best for me:
Scenery mode=Twilight (slow shutter)
Exposure EV=0
Focus=Multi Auto Focus
White balance=Fluorescent
Size=1600x1200
Fine mode
Sharpness=0

Battery life is great on this camera.

I love digital photography, I'll shoot a memory stick full ~30 pictures download them and blow the ones I don't like. I'll then tweak the ones I like in Paint Shop Pro.

Side benefit of the Sony camera:
You can even use the camera as an external storage device. I'll copy a large file (up to 32 meg) from my downstairs PC to the camera using Explorer. The camera actually becomes a drive on the PC. I then dump the file to my upstairs PC (you have to install the USB transfer software on both PCs). It's a very fast transfer.

Sony Camera at J & R Music

If you're going to buy, search the net for the best price. J & R will match the price and are very reputable.