Easy to use blenders & blurs!
Some blenders with different looks made with the basic circle tip.  They're easy to use and create decent effects.
Original on top:

Subtle Blur: Very hard to tell that it had even been blurred.  Great for light jobs.
Smear Blender: A painterly blender great for a "fingertip" effect, like you smeared thick wet paint around.

Amazingly Soft Blender: Probably more of a blur, incredibly fluffy.  A gaussian blur in a brush!
Water Drop Blend: This is a slightly harder & less extreme version of the Amazingly Soft Blender.  A bit like a water drop.

Shading Blend: A classical digital coloring blend, good for shading smooth without blurring too much.  
Snowstorm Blender: A particle blender.  Feel free to change the particle size.
        will it blend???