Just thought I'd offer a quick reference for some standard aspect ratios for your renders. I only have the free version of TG2, so I'll reference them all from 800 pixels wide. Just lock the aspect ratio if you want to adjust the width for your own renders.
1.33:1 - 800 x 600 - (Standard 4:3 aspect ratio of television and internet monitors)
1.5:1 - 800 x 533 - (35 mm film, the aspect ratio of most photographs)
1.66:1 - 800 x 482 - (35 mm film, standard cinema screen size)
1.77:1 - 800 x 450 - (16 x 9 widescreen format of most DVDs)
2.35:1 - 800 x 340 - (Panavision or Cinemascope widescreen of the old time epics)
Note: the math for these calculations is as follows, if you want to figure out your own aspect ratios.
width x (1 / width_ratio) = height
800 x (1 / 2.35) = 340
Hope this is helpful. More information can be found here:
http://en.wikipedia.org/wiki/Aspect_ratio_(image)#Previous_and_presently_used_aspect_ratios