I bought one of these bad boys last week: http://www.shop.bt.com/products/bt-i-plate-58LT.html

They claim it can boost your bandwidth by a few Mbps. I was very sceptical but I figured that for 11 quid it would be worth it if it worked.
Well, I fitted it to my phone socket 4 days ago and power cycled my router so that it re synced with the exchange and I've been monitoring it ever since. I'm glad to say that I've gone from 5.2Mbps to the full 8Mbps I pay for
V Nice!!

If you've got ADSL on a normal phone line and have the right kind of socket (check the instructions on the page) I'd recommend you invest.
I should imagine that for anybody on up to 24Mbps ADSL you should be very pleasantly surprised.