Update - The founders of HD, Toshiba, have announced the abandonment of the HD playback format as a result of poor sales which means that Blu Ray (like VHS against Betamax video in the early 80's) are the survivors of the HD revolution. In short the Playstation 3 or a stand alone Blu Ray player is all that is required now.
Update - HD upscaling Freeview boxes are becoming more available and are definitely worth considering. Although they only upscale to 1080i and not full HD (1080p) the picture quality is excellent. They are currently retailing for around £60 upwards.
Just because a television is High Definition ready doesn't mean everything it displays will be in high definition. You will still need an high definition feed from either a decoder like Sky or a games consule.
At present there are various ways to enjoy High Definition television. The best at the moment is SKY HD as it not only provides a vibrant crisp picture but also has a recorder built in which will allow 2 simultaneous recordings from 2 different digital channels but there are other broadcasters working hard to compete in this market so stay tuned and I will update.
Currently without counting promotions you will pay £299 for a box and an extra £10 a month subscription. I should mention that only HD channels will display HD quality at 1080i and there are around 15 now including sports and movies.
Playstation 3 is also capable of playing Blu Ray discs which is another form of HD. These 2 formats replicate the VHS v Betamax saga in the early eighties. Whether one will become obsolete over time remains to be seen. The Playstation 3 retails at around the £399 mark but also doubles as a superb games console.
The Xbox 360 cannot play HD discs but there is a player which can be added on at the very reasonable price of around £134. Don't get confused over the formats though, HD is totally different from Blu ray and one wont play the others discs.
HD upscalers are definitely worth a mention. These units connect via the HDMI socket on your television and convert/upscale normal DVD's to near HD quality. Now I am not saying these things are perfect but trust me they make a fine job on any film newer than 20 years old and is an excellent way of viewing HD without the expense. You can expect to pay anything from £80 for an upscaler.
Samsung and Panasonic have some lovely products including a wireless surround sound home cinema system with 1080p upscaling capabilities.
I should mention that the quality of HD depends on the capability of your television. Full HD is 1080p resolution and many televisions can't accommodate this, 1080i being the norm at present. To be honest the difference is negligible and my own view is that by the time everything has settled down and been perfected we will all need new sets anyway so don't panic if you have just forked out a small fortune for a set that only displays 1080i.