Lineone

Incoming: pop3.lineone.net
Outgoing: smtp.lineone.net

Tiny World

Incoming: pophost1.tinyworld.co.uk
Outgoing: mailhost.tinyworld.co.uk

Tiscali

Incoming: pop3.tiscali.co.uk
Outgoing: smtp.tiscali.co.uk

Yahoo

Incoming : pop.mail.yahoo.co.uk
Outgoing : smtp.mail.yahoo.co.uk

IC 24

Incoming: pop3.ic24.net
Outgoing: smtp..ic24.net

BT OpenWorld

Incoming : mail.btopenworld.com
Outgoing : mail.btopenworld.com

Supanet

pop.supanet.com
smtp.supanet.com

Free UK

pop.freeuk.net
smtp.freeuk.net

Freeserve/FSLife/FSNet/FSBusiness

pop.freeserve.net
smtp.freeserve.net

Freenetname

POP3 mail.freenetname.co.uk
SMPT smtpmail.freenetname.co.uk

NTLWorld
pop.ntlworld.com
smtp.ntlworld.com

One2One.net
mail1.one2one.net

BlueYonder/Cableinet/Telewest

pop3.blueyonder.co.uk
smtp.blueyonder.co.uk

MailAndNews.com
mailandnews.com

Ciudad.com.ar/Prima.com.ar
pop3.ciudad.com.ar

Screaming.net
pop3.uk.worldonline.com

PlusNet/Plus.Com
mail.plus.net

MyRealBox.com
pop.myrealbox.com

Setarnet.aw
mail.setarnet.aw

Totalise
mail.totalise.co.uk

Bizonline
mail.bizonline.co.uk

OneTel
mail.onetel.net.uk

Orange

pop.orange.net
smtp.orange.net

imap.orange.net is also authenticated SMTP with orange allowing sending of mail to non-orange accounts so it's a totally free email solution with no ISP buy in required.

IC24 Scotland

pop3.icscotland.net
smtp.icscotland.net

InTalk

in.talk21.com
out.talk21.com

Cix (now Nextra)

SMTP mail.cix.co.uk
POP3 mail.cix.co.uk

whsmithnet

pophost1.whsmithnet.co.uk
mailhost.whsmithnet.co.uk

UK online

pop.ukgateway.net
smtp.ukgateway.net