Claranet

View installed products
Upgrade memory and diskspace on the fly (VS only)
Set and modify reverse DNS
Reboot the server
Reimage the server
Set automated scheduled backups (VS)

Plesk

From £5 per month (10 domain license). More options below
Makes the set up of websites/email accounts/DNS and reseller accounts easy
Available with CentOS, Fedora and Windows
More information here

cPanel

£15 per month for VS or £25 per month for dedicated*
Makes the set up of websites/email accounts/DNS and reseller accounts easy
Available with CentOS Operating System
More information here

Plesk Options

Plesk allocate their licenses by the volume of domains you need to use. This starts at a 10 domain license for £5 +VAT per month. You can upgrade seamlessly to a 100 domain license for £20 +VAT per month or unlimited domains for £30 +VAT per month or just start at either of these to from the outset. These costs are in addition to your standard monthly server cost and are quoted excluding VAT.

*Costs are quoted excluding VAT