I recently bought a Sony KDL EX720 - 46inch TV. I have a HD connection from Tata Sky. I love the TV and quality. I am now pondering what additional stuff I need.
1. Is Home Theatre really needed (like Onkyo S3400) or a Sony DAV-DZ840K OR can live witha min HiFi System like MHC-GZR888DA.All the systems I have mentioned are more or less in the same price range. Incidentlally noone at my place including myself blast music or sound . Would both (Home Theatre Systems and Hifi Ssytem) provide HDMI?
2. Is Blue Ray a Must? What is the value add?
3. Are there anything additional I need to cpmplement my TV with?
Any help appreciated.
I will add my own
2 paise worth comments:
Congrats on the HD-TV. I must get one myself.

I suggest that you live with your current setup, i.e., HD-TV and TataSky HD for a couple of months and see how it goes. You can always add an HT later.
If you really wish to treat yourself, stay away from the Sony. The Onkyo S3400 is anyday much better. The disadvantage of an HT is that, you should ideally have a closed room. For example, if you install an HT in the hall, where there are only three walls, the surround sound kind of gets lost. But this is my personal opionion.
Another issue with HD sound is that the surround sound towers over the dialogues/speech. You have to turn on the volume to hear dialogues and when the surround sound kicks in, the decibells rise. This causes disturbance to others who are not watching. So that is why I say, the room should have four walls.
Good HT systems have a feature called dynamic sound control or midnight cinema that reduces the bias to the surround channels and thus cutting down on the surround sound output. But this can also be a kill-joy.
Is Blu-Ray player a must? No absolutely. But true 1080p source with true HD sound (i.e., Dolby TruHD or DTS-HD MA) is a must if you really want t enjoy the HD-TV. But such true source is available on BDs or BD-rip downloads. The TS-HD will give you 1080i picture (nearly as good as 1080p) but Dolby Digital 5.1 sound (not true HD sound but still good enough).
BD-rips have a fairly large size and downloading them will take a lot of time (unless you have a really fast Broadband). Since this is a piracy issue, I will not say much on this.
Blu-ray players are cheap, you can very well buy one just in case. But as baiju said, BDs movies are expensive - my average cost of each disc works out to Rs. 800 (I have 95 titles).
Your TV is I think a 3D-LED. So if you buy a BD player, make sure to buy a 3D BDP.