Check this out:

http://www.brill.nl/discovering-imperialism#TOC_2 [5]

There are many new translations of Pannekoek previously unavaliable in English that are now available in this book. If you want, I have scanned them all - and put one to Libcom. 

The book has the great merit of situating the intellectual debate around the concept of imperialism into the wider international context of left-internationalist social democratic milleu. So the role of the Bremen tendency (including Pannekoek and Radek) becomes clearer.

Also it presents hindsights about how this tendency infuenced Lenin and the Bolshevik-left thought deeply. I think this is a further indication of Schurer thesis which argues that Lenin and Bolshevik theory has been influenced a lot by this Bremen tendency which supported them -unlike Luxemburg- in the International. Their collaboration started from 1910 on when the left gradually started to dis-attach itself from Kautsky under the theoretical leadership of Pannekoek. In Zimmerwald they were definitely united (Bremen left and the Bolsheviks were the left wing of the zimmerwald who published a journal under the editorship of Pannekoek and Roland-Holst). And... we know how their ways parted...

There are many more interesting stuff in this book. I highly recommend it for the comrades in the ICC and sympathisers.