Not a pension guru so otheres will comment on your best options, but if you have any capital at all and you have paid down your short term debts then a SIP )sel invested pension) lump sum and getting in the markets right now would be a geat idea. At 20 you have 40 years of growth and you will never (and I mean never in those next forty years) have a better time to start geting into the markets.
Best thing for you is to set up a stakeholder pension. Interactive suggested a SIPP which is fine, but they are ideal for people with a good knowledge of the markets and who can afford higher annual charges. Stakeholders are simple, cheap and tax efficient.