BT Infinity
Only downside is that they restrict torrents a lot of the time, although where there's a will
Other than that, been hard to fault it - speed might dip a little in the evenings but not so you would notice - most speed tests are 37.5 down, 8.4 up or thereabouts. For £25 a month and also bearing in mind it's now uncapped I can't complain......
Before I moved back to BT I was with another ISP that also did FTTC (which is what Infinity is), and moved to BT because it was £10/month cheaper. A bit nervous about moving, so many horror stories etc, but as it turned out the Infinity service is a) a bit faster and b) more consistent than the previous one.