I actually booked a ticket before spotting this post. We're travelling from London St Pancras to Berlin on 21 May 2009, returning 27 May 2009. I booked at
www.bahn.co.uk and the total cost was 243.50 Euro (tickets 236 Euro, reservations 4 Euro, postage 3.50 Euro) travelling on the 08.34 Eurostar to Brussels, ICE to Cologne and then ICE to Berlin and the same in reverse coming back.