For the wider image for video, definitely have a look at the Tokina 11-16mm. It is an awesome wide angle lens, everyone will recommend it to you.
To replace your 18-55mm, it really depends on what you are looking for. I think there are three upgrade paths you need to consider:
- Prime lenses (fixed focal length): They are inexpensive, have high image quality, great low-light performance and make it easier to throw backgrounds out of focus. For that you sacrifice the ability to zoom. Have a look at 30mm or 35mm prime lenses, this is a great focal length for a first prime because it is very natural and versatile. Usually they also have great macro performance.
- Focal range: The opposite is to consider a wider focal range like a 15-85 or 18-200 type lens. You won't get better images than your 18-55 though, and often the image quality will get worse (less sharp and more distorted). I would only go down this path if you need a compact travel set up.
- Aperture range: A solution that sits in between the previous two is to stay with your current focal range but get a lens with a larger, fixed aperture. A lot of people will recommend the Tamron 17-50mm f/2.8 for example. You'd get closer to the performance of a prime lens while keeping the flexibility of your current 18-55.
Personally, I'd recommend you try an inexpensive prime to see what the fuss is about, before committing to more expensive lenses.