I'll preface this all with the following warning:
wahmbulance WARNING! THESE BOOKS ARE BEING SOLD OFF AT THESE LOW PRICES FOR A REASON: THEY WILL SOONER OR LATER BE REPLACED BY MORE UP TO DATE BOOKS. WHILE THE FLUFF REMAINS UNCHANGED, THE RULES IN THESE BOOKS ARE OUTDATED. wahmbulance
So, if you want to pick up the books for the rules, DON'T. If you're looking at picking them up for the fluff, background info and whatnot however, these are steals.
http://www.forgeworld.co.uk/New_Stuff/IMPERIAL-ARMOUR-VOLUME-EIGHT---RAID-ON-KASTOREL-NOVEM.html
Orks versus Elysian Drop Troops & Raven Guard (also comes with a free A1 sized poster)
£40.00
http://www.forgeworld.co.uk/New_Stuff/IMPERIAL-ARMOUR-VOLUME-ELEVEN-THE-DOOM-OF-MYMEARA.html
Eldar versus Cadians & Elysians & Space Wolves
£25.00
http://www.forgeworld.co.uk/Warhammer-40000/Imperial_Armour_Books/IMPERIAL-ARMOUR-VOLUMES-NINE-AND-TEN---THE-BADAB-WAR.html
Two books detailing the Badab War (also comes with a A1 sized poster showing off the Badab sector star map and IIRC a slipcase for both books)
£35.00
The Official Warhammer 40,000 and Tabletop Gaming Guild
The Official Gaian Home of Tabletop Gaming