I'm implementing an up/down voting system, and I want to find a standard but sleek button with an arrow inside it that you can customize by color, arrow size etc.
Are you doing this in html and css? Do you need the shape to adapt dynamically on site? You could use the htmlentities and get these: ← ↑ ⇐ ⇑ You could then change size and color with css font-size and color. http://htmlhelp.com/reference/html40/entities/symbols.html
Otherwise I would do as Nikhil Singh suggests. It is far easier and definitely faster to do some arrows yourself.
I face the same issue time and time again. I think it's best to make your own arrows. They're pretty basic shapes that can be constructed easily in InkScape - (which is free), or Illustrator/Corel Draw.
You can then color them to your liking, export 2 png files - one for static and one for mouse over state.
Hope this was of some help.