This massive 400GB Seagate External USB 2.0 Hard Drive is only £149.99 delivered from maplin. I believe you can get this even cheaper if you sign up (or already signed up) to their newsletter - £7 off this price (every little counts!).
Seagate are a very good make when it comes to hard drive technology.
Details: • High speed USB 2.0
• Sleek elegant structure actually dissipates heat so they run much cooler than any other external drives
• Hot-swappable so you can connect and disconnect without turning off your computer
• 7200 RPM spin speed
• Masive 16MB cache on this 400GB model
• 350Gs non operating shock resistance
• Whisper quiet acoustics
• Push button backup
• Award winning Bounceback express software
• Diagnostic software included
• Approximate dimensions when horizontal: 7.125” D x 6.5” W x 2.25” H
• Approximate dimensions when vertical with pedestal: 7.125” D x 3” W x 6.75” H
• Weight: 2lb, 9.5oz