Groupon again... Whilst checking if the Harman Kardon offer was still around I came across this. It's certainly not the best speaker out there but I'd really struggle to think of anything that can compare for the price. I got one from HMV a couple of years ago for £20 and it's still going, despite several holidays and boozy garden parties. It's pretty much perfect to chuck in a bag.
Despite my recent experience with Groupon, I've ordered this as it's good even just for having a spare charger.