A little-known fact about the movie American Beauty: there was an extended ending that was never aired to the general viewing public, and left off the "extras" section of the DVD. There was an extended beginning too, but I don't know anything about it. They left the endings off the final cut because they felt that it unnecessary, since the movie was primarily about Lester, and anything more would simply detract from the overall aim of the film. I hope to offer some insight into these extended endings, regardless of the fact that I've never witnessed them firsthand. All my information is collected from various second-hand sources, so take this information with a grain of salt...
The extended ending consisted mostly of the trial of Ricky Fitts (Wes Bently) and Jane Burnham (Thora Birch) for the murder of Lester Burnham (Kevin Spacey). There were two possible outcomes that they had filmed.
In one alternate ending, Ricky and Jane are found guilty of murder, and both are sentenced to life in prison. Their conviction and sentencing is a result of Ricky's videophilia, as his entire videography is submitted as evidence. The movie ends with Ricky in a prison cell singing "Us and Them" by Pink Floyd. Zoom out, cue Lester and his treatise on life.
The second alternate ending is similar to the first one, but the outcome of the trial is different. Barbara Fitts (Allison Janney), the mentally unsound wife of Col. Frank Fitts (Chris Cooper), submits as evidence the bloody shirt of her husband, the murderer. This evidence is sufficient to convict Col. Frank Fitts of the murder of Lester Burnham.
From what I know about these endings, it seems that Sam Mendes didn't feel that it was necessary to have the longer ending(s), and that it would detract from the credibility of the film. I suppose he's right, since both of those endings would be too... final, I guess. They're just not the right way to end a film like American Beauty. Regardless of their cinematic value, it's an interesting tidbit of information.