I'm looking for a good action/sports lens for a Nikon thats under $500?

Sports like, baseball, basketball, football, and soccer. I'm looking at the D5100 by the way, I would very much like your opinion thanks!

Tamron SP AF 70-300 F/4-5.6 Di VC USD

USD = Ultrasonic Silent Drive = very speed autofocus

While the Number 1 sports lens is a 70-200mm f/2.8, it is far over your budget.

The best telephoto lens in your budget will be the Nikon AF-S 70-300mm f/4.5~5.6.It's performance will not be as good as a 70-200mm f/2.8, but in daylight situations it will work. Inside venues, such as basketball may be though though as the lighting is not as good, which usually requires the 70-200mm f/2.8.

While the Nikon lens is just above your budget at $580, you can buy a refurbished one for under $400.

http://www.adorama.com/...AFVRR.html

I have bought several refurbished lenses without any problems. Just make sure they are factory refurbished rather than dealer refurbished. Factory refurbished lenses are checked out by Nikon and are repaired, aligned, and calibrated if need be, and due to manufacturing tolerances, can even be better than lenses coming off the production line.

When buying refurbished Nikon lenses, you can get a Nikon for no more, or even less money than a lower quality (new) Sigma or Tamron.