I'd favour the Abus Granite 54 x-plus over the Knog at that price point - £56 @ Abus Granit-54 X-Plus: Amazon.co.uk: Sports & Outdoors
The Kryptonite new york 3000 is currently £47 on amazon ( although see Captain cropper's comments about it here http://www.bikeradar.com/gear/category/accessories/locks/product/review-kryptonite-new-york-3000-10498 ),
and the new Onguard Brute seems a bargain at £24 for a gold rated 16mm+ lock Magnum ONGUARD Brute STD Bicycle Security Bike U-Lock LK8001: Amazon.co.uk: Sports & Outdoors
Manufacturer's brochure here:- http://onguardlock.com/wp-content/uploads/2013_OnGuardCatalog_NEW_web.pdf
If you haven't already read it, there's a good article about bike locks here http://www.ctc.org.uk/sites/default/files/file_member/200803042.pdf
@lemonaid started
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I'd favour the Abus Granite 54 x-plus over the Knog at that price point - £56 @ Abus Granit-54 X-Plus: Amazon.co.uk: Sports & Outdoors
The Kryptonite new york 3000 is currently £47 on amazon ( although see Captain cropper's comments about it here http://www.bikeradar.com/gear/category/accessories/locks/product/review-kryptonite-new-york-3000-10498 ),
and the new Onguard Brute seems a bargain at £24 for a gold rated 16mm+ lock Magnum ONGUARD Brute STD Bicycle Security Bike U-Lock LK8001: Amazon.co.uk: Sports & Outdoors
Manufacturer's brochure here:- http://onguardlock.com/wp-content/uploads/2013_OnGuardCatalog_NEW_web.pdf
If you haven't already read it, there's a good article about bike locks here http://www.ctc.org.uk/sites/default/files/file_member/200803042.pdf