Need "Entry Level" D-SLR

[erikzen]

Here is yet another "help me choose a camera" thread.

I am in the enviable (unenviable?) position of needing a camera for my business. Part of what I do is organize an annual conference for a trade association. The board members like to have lots of photos of their events so attendees can get that warm and fuzzy feeling post-conference and also to use in futue mailings and on the website. I also do other marketing work for clients and have to come up with mailings, print ads, banners and other marketing materials from time to time. Often I can use stock images but there have been occasions when I need to get my own image. So there is a real business need for a decent (but not pro-level) camera. I have various point and shoot cameras which I've gotten by with but I'm not always pleased with the results. Zoom is not good enough and lighting conditions are not always ideal.

In addition to typical conference shots of speakers and members during cocktail hours, we will also be holding a reception at the National Aquarium in Baltimore. I can imagine some interesting shots with the various animal life and the members, but I know from experience at home that photographing fishtanks is a challenge.

This is starting to ramble a bit so let me try and get to the point:

-I need a camera that produce can decent images for web and print work (relatively small size images)

-Budget is entry level. It should be less than $750 if possible. Cheaper is better. Although it's a business expense the cost still comes out of my profits, so to speak. Used is OK. Then again if spending an additional $200 gets me a great piece of equipment that's going to last many years, I don't want to be pennywise and pound foolish.

-Should give decent results in challenging light situations

-Is there a camera (or technique) that is suited to shooting aquariums?

-I have some photograpy experience (35mm SLR and P&S digital) but I am definitely an amatuer.

-I am comfortable working with a computer and have some PhotoShop experience and work with a designer that is a PS power user.

Cameras that look reasonable and in the right price range that I've looked at online are:

Nikon D40
Canon XTi
Sony Alpha 100/200

My next step is to go to a camera store to try and get a feel for what I like, but I'd like to have some kind of idea going in.

Any advice or suggestions is appreciated.

Is something like the Nikon D40 a good choice? Canon XTi cameras seem to be well regarded.