11×8.5  
Typically printed on letter sized posterboard with a home or office printer

28×22  
This is normally a posterboard size

96×48  
This is a really big corrugated plastic size

14×8.5  
Typically printed on legal sized posterboard with a home or office printer

17×11  
Typically printed on tabloid/ledger sized posterboard with a medium format home or office printer

17×5.5  
Print on 17x11 posterboard and cut lengthwise to make two medium-sized dashboard signs

18×12  
This is normally a corrugated plastic size

22×14  
This is normally a posterboard size

24×18  
This is the most common corrugated plastic size

24×9  
This is normally a corrugated plastic size

26×16  
This is the most common polybag size