I've recently changed over from tiscali to O2 broad band. Tiscali applied an upgrade to my service that my line was incapable of handling and failed on numerous occasions to sort the problem out so I was left with a service that was highly unstable, speeds going up and down rapidly and generally leveling out at something stupid like 10KB/s. So I decided to switch to O2 the incentive being that I am a mobile customer and get it cheap. the first difference I noticed was that O2 has a free phone number for customer support (compared to the 0870 number for tiscali) and you speak to someone who's first langauge is english! not only that the guy I spoke to knew what he was talking about when I explained the situation. I migrated over a few days ago and the difference is incredible! The router they provide isn't too bad, you get McAfee virus guard for as long as your with them to.
Can't recommend them enough.