Best videos on YouTube for learning to roll (for sea kayakers)

There are lots of ways to roll, and lots of ways to teach rolling. While there is no substitute for a 1:1 lesson with a good instructor, it can be really helpful to get the theory internalised first, to make the most out of time training in the water with either an instructor, or a learning partner.
If you watch these videos, and run through the motions in your mind, and visualise yourself doing it in real situations, that can be a great head start.

Whatever style of roll you try, it is all about technique, not about power. Essential to that technique is torso rotation and flexibility. Here's a great video with a number of stretching exercise that we can all practice every day, whether we are on the water or not.

It is also possible to practice rolling in your boat on dry land; it is particularly useful for working on the knee/leg actions required, and for building up muscle memory. 

In this video, she is demonstrating a C to C roll, which isn't my preferred roll for a sea kayak, but the leg movements are the same, and it is still good practice.

There's another dry land practice technique demonstrated in this video. Getting things like this down well first will let you get the most out of your time in the pool.

Everyone will eventually find a style of roll that suits them and their chosen field of kayaking, but for sea kayaking, I find the sweep roll most effective, and this video is the most comprehensive analysis of the sweep I've seen.

Here's another, far more concise take on the sweep roll. As you can see, she's using almost no strength at all. In fact, she makes it look effortless, which it should be if all of the elements of body movement are done right.

I prefer the sweep for sea kayaking because it is slower, and distributes the righting effort more evenly over the entire action. This is relevant because very often in sea kayaks we have camping gear, food, water, emergency equipment and clothing in our boats. The gross weight of the boat, gear and paddler can be far greater than you would ever see in a white water boat (like in the video above). In this laden condition, placing all the righting effort into one jerk, as in the C to C or EJ's "head down and hips" roll, may not be effective, or may over-stress the body in places.
Even if you aren't carrying lots of gear, the surface area of a sea kayak is far greater than a short boat, so there can be more drag from the water. Coming up more slowly and gently is usually the better option.
That said, in rock-hopping and surf zones, particularly if using a play sea kayak like a Dagger Stratos or P&H Virgo, a C to C or hip-snap roll will probably be fine.

Here's a set of 3 videos that also teach the sweep roll from scratch. These were all filmed in a pool, and demonstrate really well how people working in pairs in a pool can coach each other to rolling confidence, even from a very low base.

And another, more concise run through, of how to teach the roll.

An an example of beautiful technique. See how slowly and gracefully he comes back up, almost no effort exerted.

Troubleshooting.

Once the basic roll is accomplished in the pool, it is essential to keep practicing. Rolling is the most perishable skill I know of, without regular practice it just fades, and if you can't rely on it, your confidence to go where you want to go, and do what you want to do in a kayak will be diminished.

It is also important to keep adding new skills, such as alternative rolls and rolls in different circumstances. For example, the re-entry and roll is very useful to practice, as it is probably the only practical self-rescue technique for a laden sea kayak.

And well, if you have mastered the re-entry and roll, you might as well practice "The Dump" to save all the messing around with a pump.

And if you have mastered all these techniques, you're a better paddler than I am!