You'll be lucky to get unlimited for £25, for a real unlimited service you'd be looking at ~£80. Tiscali certainly isn't unlimited, you just apparently haven't hit any of their limits.
O2/Be are apparently worth looking at if you're connected to one of the 20% of exchanges that can get their proper service as they currently haven't imposed any limits as far as I know (though it's probably inevitable that they will eventually at the price they're charging).
Likewise, not everyone can get over 8Mbit/s as well so if you do look at 20/24Mbit/s be sure to check availability first.
I'm on Post Office Broadband Extra + Homephone and I've been happy with it, my maximum monthly usage has probably been around 60-70GB with no complaints from them.
http://www.postoffice.co.uk/portal/p...diaId=87500743