Cubana, the cuban goverment owned airline is the only one that provides internal flights in Cuba from Havana to:

Baracoa (US$78)

Bayamo (US$59)

Camagüey (US$51)

Ciego de Avila (US$43)

Nueva Gerona (US$16)

Guantanamo (US$73)

Holguin (US$79)

Las Tunas (US$77)

Manzanillo (US$59)

Moa (US$73)

Santiago de Cuba (US$68)

Check-in is 60 minutes before flight time and the baggage limits is 20 kilos. Most of Cubana's internal flights are on Antonov AN-24 propeller aircraft, although Yakolev YAK 42 jets are often used to Camagüey, Holguin, and Santiago de Cuba. Domestic fligts are 25 % cheaper when booked in conjunction with an international flight on Cubana. Ask your travel agent to check with Cubana about this. Inside Cuba you can often book through an hotel tour desk or a local travel agency for the same price that you'd pay at the local Cubana Office. Reserve as far in advance as possible if you want to be sure of a seat, although dollar-paying foreigners do get some preference.

For other information, but not expect nothing special, you could check their website at: http://www.cubana.cu