Since you've posted in the 'Travel' section, I'll assume that you're referring to flying. Further I'll assume that you're a UK citizen, and that you live in the UK.
For travel (with any airline) to any country other than the UK, Channel Islands or Ireland you must have a passport. There are no exceptions. (It's not an airline rule. It's imposed by the governments of the countries where the flights land).
Some airlines operating within the UK and Ireland (or to the Channel Islands) accept only a passport or photo-driving licence. (Ryanair is one such airline. From later this year they'll no longer accept driving licences. It will be a passport or nothing).
Other airlines (with the UK/Ireland/Channel Islands) are more flexible. For example easyJet will accept almost any form of photographic ID (including, for example, a bus pass). Others might fall somewhere between the policies of Ryanair and easyJet. (i.e. they'll accept a more limited range of types of ID than easyJet but not as restricted as Ryanair).
Without knowing who you wish to fly with it's not possible for anyone here to advise you specifically as to what type of ID you should seek out. Boo's link is a good one; a Citizen Card might be accepted by several airlines (although obviously not by Ryanair) but it would be pointless applying for one unless (as Boo suggests) you've checked the specific requirements of the relevant airline first.
Chris