From Macromedia's Flash Authoring Guidelines (width x height):
Wide skyscraper 160 x 600
Skyscraper 120 x 600
Half-page ad 300 x 600
Full banner 468 x 60
Half banner 234 x 60
Micro bar 88 x 31
Button 1 120 x 90
Button 2 120 x 60
Vertical banner 120 x 240
Square button 125 x 125
Leaderboard 728 x 90
Medium rectangle 300 x 250
Square pop-up 250 x 250
Vertical rectangle 240 x 400
Large rectangle 336 x 280
Rectangle 180 x 150
Signatures Only Shown Once
No Yes
If this option is set to yes then signatures will only be displayed once per page.