One of the main problems that filmmakers with a very small budget have is sound quality. While you can do certain things to make your video look better, there are certain times when there's nothing you can do about bad audio. Maybe the on-board microphone picks up camera noises, or just tends to hiss a lot, one great solution is to purchase a cheap lapel mic to fix some of your problems.
Last year, I was searching for a cheap audio solution, when I came across the Audio-Technica ATR-3350 on Amazon for around $20. After watching a few test videos, I purchased one of these, and have definitely gotten my money's worth out of it. The microphone has an extremely long cable allowing you to stand a far distance from the camera and still pick up good audio quality, without all of the normal hiss.
For only $20, don't be expecting it to sound as blissful as a Hollywood movie, as it does still have some background hiss, but I found a certain setting on my editor that cleared the hiss up terrifically. But, as low as the price is, it far exceeds the quality of most camera microphones and is well worth it. One downside is that you do have to have a separate recorder to record the audio if your camera doesn't have a "Mic In" port, but I believe it is well worth the extra trouble to get better quality.
So, if you're in need of a cheap audio recorder just to give your video a little more professional quality, look no further than the Audio-Technica ATR-3350. For a cheap price, you get solid sound quality, and it far exceeds the ability of any normal camera microphone.