I copied this list from another post here on the DIS. Hope it helps:
Alamo; At Car Care Center; M-F 6am-8pm, Wknd 6am-6pm; 407-824-3470
Alamo; In Buena Vista Palace; 8am-4pm; 407-827-6363
Alamo; In Dolphin Resort; 8am-4pm; 407-934-4930
Avis; In Hilton at WDW; 8am-6pm; 407-827-2847
Budget; In Doubletree; 8am-5pm (closed holidays); 407-827-6089
Dollar; In Regal Sun Resort; 9am-4pm; 407-583-8000
Enterprise; In Marriott World Center; M-F 9am-5pm, Wknd 9am-1pm; 407-397-0800
Hertz; In Shades of Green; 8am-5pm; 407-938-0600
Hertz; In Caribe Royale; 8am-6pm; 407-239-2502
National; At Car Care Center; M-F 6am-8pm, Wknd 6am-6pm; 407-824-3470
National; In Buena Vista Palace; 8am-4pm; 407-827-6363
National; In Dolphin Resort; 8am-4pm; 407-934-4930
Thrifty; In Radisson Celebration; 24hr; 407-390-1596