I'm looking for a dedicated hosting to build a huge site which includes streaming videos and live conferences. Any idea which host I should go for?
Dedicated hosting is pretty pricey, I don't think you'll be able to find anything below $120 - 140 a month for specs like

2.3GHz CPU
100 mbps Uplink
4 GB Ram
500 GB storage
10 TB Bandwidth
Up to 5 Dedicated IPs

This is hostgator's cheapest dedicated plan. Actually I recommend them for any type of hosting. Dedicated hosting is more pricey than shared or VPS because they give you dedicated hardware somehow like leasing an actual physical server and they maintain it for you to an extent.

Choosing which plan to go for depends on what you are going to build and how "large" is your web application and what do you need from it. Most of the time a VPS(which is cheaper) can be enough for most needs. Here is a nice and clear explanation about the differences between between a VPS and a dedicated server plan. I suggest you give it a read.

Also before choosing any plan make sure you decide based on the requirements from your final website which directly reflect the specs and needs from a server:
- Which framework/technology the web app is built in and how much resource intensive would it be
- Will you install additional web apps on the server such as cpanel?
- Which Linux distribution are you planning to install and work with. Will you want to install a GUI or administer it from the terminal.
- How much traffic are you expecting to have in the beginning? How many live users are you expecting? (can directly affect your RAM, bandwidth, processing and IO)
- Will you perform caching on your site's content?
- etc...

I think its better to start off with a relatively cheap VPS plan, as needs grow you upgrade your plan until it starts to make sense moving to a dedicated host in terms of the cost/benefit.

A third option you may want to consider is cloud hosting such as AWS, Rackspace or Heroku(which is awesome but pretty pricey). These are more pricey in general than a VPS but generally more scalable, secure, reliable and performant (of course as long as you keep paying as your needs grow). And they abstract a lot for you in terms of hardware, maintenance, deployment and administration so you can focus on your web app. You can read about cloud hosting and its advantages a lot if you search.
Thanks, Ayman. What I'm looking to build is a community website that links people of a school together. Not a facebook clone, something that involves remote access and live lectures.
You can try hetzner.com if you're targeting Europe/Middle East, they are geographically closer (lower latency) and cheaper than USA hosts..

Also if you're going to have a lot of videos streaming going at once, I suggest you get your server connected to a 1Gigabit port instead of the default 100 Mbps
@Nabs: You might be interested in BigBlueButton, it's open source and is relevant to what you're trying to do.
There is a point where going towards EC2 (or Google's new compute engine) is better in terms of price and scaling potential than going for a dedicated box. You need to give us more details as to what you are building and what you need in terms of resources. If the system is bandwidth-heavy but is only used by a small audience, it might make more sense to serve the main site via a cheap VPS (you can find one through venam's link) and the bandwidth heavy stuff (like the videos) via Amazon S3 for static files and Cloudfront for streaming.
Describe what you are building in more details.
@Samer, it's a website for multiple universities, where student can attend online joined coursed and watch lectures, commence in video calls and ask teachers questions, have video conferences, watch stuff from the archives...
Have you secured deals with universities? If so, how many? If you just want to build and host a prototype, go with a VPS or use the amazon free tier. No need to worry about scaling until you have a couple of universities and several of their courses on-board.