The link to online check-in is now on the Ryanair homepage. One potentially expensive term to note:
Any passenger failing to present their printed Check N’Go boarding pass at airport security and the departure gate will be charged a boarding card reissue fee of €20/£13.50 per person.
So don't go losing that piece of paper (and check your printer works before you check-in online!). Additionally, if you change your mind about travelling with hand baggage only or your hand baggage exceeds the permitted weight/dimensions, then you'll have to check-in as usual and pay the above charge.
I guess that at least it's cheaper than replacing a lost traditional ticket though.