I'm a new guy around here but I have a lot of experiance with dvd burning so here's my .02
What you use for blank media makes all the difference in the world when burning movies. Most of the "name brand" discs are crap for movies and Memorex is the absolute worse, I won't use them if someone gives them to me. You may get a good batch of "cheap disc" but you never know. If you stick witht he good stuff from a reputable dealer you always know what you are getting.
I almost always use Ritek Ridata "branded" 8x +R. I have burned over 200 movies and never had a coaster that wasn't my fault. A slower burn is better when doing DVD's I usually burn at 2.4X sometimes at 4X but never faster than that. Ritek Ridata "branded" 8x +R are top of the line discs for movies and they are cheaper than most I get them through meritline.com a very good and reliable company with an outstanding return policy.
Another choice that you can get at Best Buy if you don't like to shop over the web is Verbatim "datalife" (they look like old movie reels on the top of the disc), Not all of the verbatim are the same either, these are the only other ones I use.
You can also use TY's but the ones that are good enough for movies are expensive
Here's a link: http://meritline.com/ritek-8x-dvd-plus-r-dvdplusr-branded-blank-media-discs.html