I'd recommend the Kenko tubes too
Ive read some good reports about the Kenko tubes, but for £140 they are a bit out of my price range as ive had a bit of a spend up recently on other camera stuff.
BUT ... if they are far better than the cheaper ones, then it will be worth waiting for it ...
Better look into this a bit more indepth. I dont want to end up with rubbish, then have to go out and replace and end up spending more. learnt the hard way, so maybe its best to save and get the Kenko