In reply to aujayeb: There is no single rope that is ideal in all situations but at the risk of opening up a "can of worms" here is my advice.
For UK trad none dry treated 50 metre half ropes are best/cheapest and suitable for single pitch.
For ice I would use dry treated 60 metre half ropes.
For sport a 60 metre single will be enough in most situations but if you are going abroad 70 metres is better. For multi-pitch sport and continental ice falls 60 metre twins are also an option but halves are possibly better.
Just to confuse matters there are now ropes available that are rated as single, twin and half. If you can only get one rope tyhis might be worth considering but you will pay a little more and it will not last as long as some of the others. In general heavier ropes last longer.
I think Mammut and Edelrid make the best ropes. Beal feel nice but everyone I know who owns one says that they are not long as lasting.