These are some popular sources of video online
You can subscribe to Netflix. They originally sent out one or two DVD's at a time, as a video rental service. You could get most any movie out there, and keep a list of what movies you were interested in seeing. You could keep the moview as long as you wanted. When you returned one you would get the next one in your list.
This worked out pretty well. The key to the whole thing was that the founders of Netflix had noticed that the postage to send a DVD, without the box, was only 45 cents (standard first class mail).
Apparently the cable companoes weren't happy. They apparently lobbied the postal service and got the rates raised, so that Netflix has to pay double rates, with the thin excuse that any letter that isn't bendable, should pay more. I can't think of any reason for this. Personally, I think they should raise the rates on all the people sending me junk mail, and they should be happy that Netflix is bringing them so much businesss.
In any case, when the USPS raised their postage rates, Netflix responded by offering videos online. This service works pretty well, but the selection is very limited. A while ago they raised their rates. Originally it was $14 a month for two vides at a time. So you could see ten or fifteen videos a month for this price. Then they added online videos, and raised the total rate to $24 a month. I decided this was two much and cut my subscription back to one video at a time, at ten dollars a month, with no online videos. I will consider adding more services when they get more online movies. Right now it just isn't worth the extra charge.
I really hate Blockbuster. Back in the day, they tried to improve their bottom line by renting out videos for cheap, then charing huge late fees instead of just extending the rental if you decided to keep the video a little longer. I can just imagine a bunch of high paid MBS's in suits sitting around a converence table thinking how smart they were coming up with this idea.
That worked great for a while, at least it made them extra money. The problem is, getting a late fee is kind of like getting a parking ticket. It makes you mad, it makes you see red, it makes you really hate them and want to see them fail.
Now Blockbuster is on hard times. They're realized that the late fees thing was destroying their customer relationships, and they've given it up. Now they offer Netflix style movie rentals with monthly charges and no late fees, and you can even go into the store and pick out something to watch, same day, which sort of gives them an advantage over Netflix. So there are some logical reasons to give them another chance.
I'm still mad at them and haven't been in one of their stores for several years. They just charged me one too many late fees.
Youtube is a great source of online video. It's especially strong in short subjects, music videos, howto videos, and home made films. Not much feature films here. You can store your video here and share it with friends. Youtube depends more on personal contributions than on corporate or network submissions.
Vimeo is similar to Youtube. It has better resolution, better quality video, but isn't nearly as popular. If you have some video you want to store, this might be a good choice because it's going to look a lot better here than it will on Youtube. On the other hand, if you are looking for old music videos or something like that, you're much more likely to find them on Youtube. Vimeo will let you upload a certain number of videos per week on a free account, or for $60 you can upgrade to the big-spender account with much higher amounts of storage.
Originally envisioned as a competitor to Netflix, this is an online only service that is mostly free, but does have some paid content too. They have some of the networks participating. They certainly don't have everything, but it's worth a look to see if they have what you want.
Much of the content of the Public Broadcasting System is available free online. For example, the "Doc Martin" show from England is fun and is free on PBS.
Pirate Bay is the original pirate video site. Pretty much everything is available here, but much of it is filled with viruses, and a lot of it is pretty poor quality too.
Other Pirate sites are also available. For example, right now you can view the latest episodes of Game of Thrones for free at http://www.free-tv-video-online.me/internet/game_of_thrones/season_2.html.
Be careful with pirate sites. Usually when I hear about people whose computers have been hacked, it's because they were trying to watch free video and one way or another they ended up installing a virus.
A general rule: if one of these pirate video sites asks you to install something, don't. There is no pirate video site that has it's own player. They don't have that level of technology. If they ask you to install something, absolutely 100 percent for sure, it is a virus.
You have been warned.