How to get the most time shooting video?

I'm just starting to shoot video with my Nikon D5100. I was recording in HD, and I only got 19 minutes. Is there a way to maximize the amount of time I can shoot for? Can I switch to SD if I'm only recording for the Internet? I'm new to this, and it seems like there should be a way to squeeze more recording time out of my camera.

Regardless of resolution and frame rate, recording times are limited to 20 minutes or four gigabytes per clip, whichever limit is reached first. Nikon hasn't explained the reason for the time limit as of this writing, but it's likely due to sensor heating issues that might start to degrade image quality.

Quote from Nikon D5100 Camera Video - Full Review

20 minutes is the limit, but if it's any consolation, I've read that Nikon's 20 minute is the longest clip time of any DSLR. So, you probably won't find longer until a new thing comes along. Of course, depending on what you use it for, 20 minutes is a long clip. All you have to do is stop and restart immediately and you're good for another 20 minutes.