Welcome to the forums. I have only been here for about a week and have learned quite a bit. That "M" setting on my A560 is a lot of fun now!!! I am in the same boat, looking for something soon to make my foray into stills but my purchase is a few months off.
Definitely go to BB, CC or where to play with the bodies. I originally was looking at the XTi like yourself and figured that would be the best fit for me (not that it is not a great starter camera) but after feeling the 5D and 40D I quickly realized how small the XTi really was and that for any extended shooting that my hand would quickly cramp.
So with that said I am going to have to go against the grain and recommend picking up a used 20/30D from somewhere like KEH, B&H or Adorama for a decent price. You can find good quality 20D's at B&H for about the same price you would pay for an XTi. Just my $0.02 but thought I might throw it out there!!!
GL and have fun!