If you are going to Cataluna then Barcalorna or Reus are the most convenient airports. From Reus you can take the bus to either Cornudella de Montsant (Siurana) or Margalef, both offering superb but very different types of climbing. If you wanna go to any other of the many crags in the area you will probably want to rent a car.
Catalunya is very large and completely stuffed full of world class climbing, so your question is rather vague.
There are now two excellent, up-to-date guidebooks (trilingual english-catalan-spanish) for Catalunya, "Lleida Climbs" and "Tarragona Climbs", by Pete O'Donovan and Dani Andrada. Both are worth the investment and will help you plan your trip. There are also dozens of previous threads on these forums, and quite a lot of information on google.