BT's Total Broadband package provides a Home Hub router that connects to BT's broadband service (a BT/Yahoo collaboration, as is the email service provided) and provides wireless access as well as VoIP (once the phone handsets arrive, anyway). I can't find details of what make the router actually is, but I think it might be a Thomson Speedtouch. It works pretty well, though the configuration options are a bit hard to find: connect to bthomehub.home and switch user to Admin to make changes; the most useful settings are those for the wireless network.
Encryption by default is WEP: use the page linked above to switch to WPA-PSK and enter a key (use a WPA-PSK key generator to get a key of sufficient length and randomness, if you like). Set the encryption to WPA only, not WPA+WPA2: with the latter setting, I couldn't get OS X to connect.
The port forwarding options allow you to easily forward ports (for Azureus, say) to specific devices.
There's an option to enable WDS and scan for available WDS-compatible devices, but I have a feeling the Home Hub only acts as a WDS client, not a bridge: I haven't been able to get an internet connection working when connecting through an Airport Express in WDS mode. The Airport Express will connect as a client to the hub anyway, although I haven't got AirTunes to work properly yet: the speakers attached will rarely show up in iTunes (they did once, but I'm not sure what was different that time).
There's a useful BT Home Hub discussion thread on Digital Spy forums.
Update... there still seems to be trouble with WPA: OS X is regularly dropping the connection every 15 minutes or so. Switched back to WEP for now (OS X also doesn't handle switching between encryption protocols very well: you have to delete the network from 'Preferred Networks' and re-add it with the right encryption, otherwise it'll claim to be connected but won't get an IP address).