Here are your options:
United (Non-stop to hundreds of cities from O'hare including Orlando)
Mileage Plus Visa:
1 Mileage Plus Mile for every $1 in purchases*
5,000 Bonus Miles after your first purchase with the card*
FREE $25 Discount Certificate on a future United Airlines flight*
FREE 1,000 Mile Upgrade Certificate*
($60 Annual fee)
http://www.firstusa.com/cgi-bin/webcgi/webserve.cgi?partner_dir_name=united_mileage_plus&page=cont
Southwest (Non-stop to dozens of cities from Midway including Orlando)
Rapid Rewards Visa:
Earn 16 credits within 12 consecutive months and you can earn a free roundtrip ticket.
Cardmembers will receive four (4) Rapid Rewards Credits with the first purchase with the card!
($39 Classic / $59 Platinum Annual Fee)
http://www.firstusa.com/cgi-bin/webcgi/webserve.cgi?partner_dir_name=southwest_airlines&page=cont
AMERICAN (Non-stop to Orlando from O'hare)
Aadvantage Visa:
5,000 bonus miles and a six month Annual fee waiver for new cardmembers.
($50 Annual Fee)
http://www.citibank.com/us/cards/sp-promo/aa5k_1/
There are others, such as Diners Club which let you use your miles on any airline, but they also have the annual fee and are accepted at fewer locations.
There are also some no-annual fee cards, but you only get .5 mile/$ spent.