Spain By Plane
Iberia and the smaller, slightly cheaper subsidiary Aviaco, as well as the independent companies Spanair and AirEurope, operate an extensive network of internal flights. While these are quite reasonable by international standards, they still work out very pricey, and are only really worth considering if you're in a hurry and need to cross the entire peninsula. The main exceptions are the route between Madrid and Barcelona, which is very poorly serviced by public transport, or getting to, and between, the Balearic Islands, for which flights are only marginally more expensive than the ferries. In peak season you may well have to reserve long in advance for these.
From North America, Central Holidays/ Discover Spain Vacations sell the Spain Airpass for $165 per flight on Iberia within Spain (in conjunction with an Iberia transatlantic flight); a minimum of two passes are required but there is no limit to how many passes you may purchase. Air Europa is a carrier offering internal flights which can be booked from North America. In Australia, the Spain Airpass is available from Spanish Tourism Promotions in Melbourne. The Spain Airpass isn't available in Britain and Ireland.
Spain By bus
Spain By train
Spain By car
Spain Hitching
Spain By bicycle
Spain By plane