If you want low friction then a trackball is your best bet.
I use this one and thoroughly recommend it:
http://www.microsoft.com/hardware/mouseandkeyboard/ProductDetails.aspx?pid=011
It's optical, is very responsive, very comfortable and you're able to control movement just by moving your forefinger (the rest of the hand fits around it). No need to keep lifting and re-positioning like with a mouse either.
I use this one and thoroughly recommend it:
http://www.microsoft.com/hardware/mouseandkeyboard/ProductDetails.aspx?pid=011
It's optical, is very responsive, very comfortable and you're able to control movement just by moving your forefinger (the rest of the hand fits around it). No need to keep lifting and re-positioning like with a mouse either.