I've listened to a few sound bars at various mates houses and all of them have been quite disappointing. Clearly they are much better than the tiny speakers built into the new TVs, but all of them seem to struggle to create a proper sound stage and really struggle in large rooms. None I've heard offer any where near the performance of a good 5.1 system driven by a decent amp (regardless of what the advertising says).
But as already said if you want good sound its not cheap, but for £300+ you should be able to get a OK AVR + 5.1 speakers, which will produce much better sound than any soundbar at that price point.
http://www.richersounds.com/package/...deals/pah01858