This is a really nice slider design with gradient colour which emphasises the progress. Designer: Ilja Miskov Source: Dribbble

Slider with gradient colour

Excellent example of a clean slider design. There is also a free PSD available too. Designer: Maki Myers Source: MakiMyers

Clean slider

This is an excellent example of slider design with an amazing colour palette. Designer: Liam McCabe Source: PixelsDaily

Colourful Slider