Which Digital Prof SLR To Buy ?

Hi everyone,
My old Canon AE1 had been passed down to my son and I’m now looking to purchase a digital SLR (not necessarily a new model) however not knowing really much about them.
Will be using the camera at a few airshows and aircraft on the approach to Heathrow and Gatwick.

Have spoken to a few guys at Gatwick , they all seemed happy with what they were using ,their cameras were :
Nikon D50, canon Eos 300D, 350D, Eos D30 and a Olympus e500 but couldn’t remember what lenses they used.

Can anyone recommend any of the above or maybe later models of the one’s I’ve mentioned and maybe what type of lens to use for what I want?

Thanks in anticipation
Tim