Octopo:
Well there are plenty of options though none much cheaper to my knowledge than the £150 or so you can buy a TVix for.
I currently use an Xbox to stream stuff of my NAS (PS3 will do the same) giving you the option of Blu-ray and games as well.
WD to a media player for about £100 though you'll need storage on top of that.
Apple TV will allow you to connect to hard drives attached to the network as well as its own internal drive for about £170.
This Linksys is a pretty good deal for £130 combined with a DVD player.
Though it all depends on how you want to set the system up. Hope this helps.
I use the Linksys DMA2100 (the same as the one mentioned but without the dvd drive). It works very well. It can also stream up to 1080p video but doesn't decode mkv (my only problem with it).