I use channel calculations for things with definable background and people or animals with fur or hair. On pre CS3.... I use magnetic lasso tool most to create my rough outlines and then go to quick mask mode where I fine tune it with a brush. I used to use magic wand a lot but discovered it was more of PITA to get a good tolerance that works for some images so I rely on magnetic lasso tool more. Either way... to get a nice clean mask... I always use quick mask mode in the end to tidy things up. I have also found its good to use an extra layer on bottom filled with black (delete on save) that helps to show just how good the mask worked before I save it out.
CS3 has that new quick selection tool which is very nice. I use it more than magnetic lasso when on CS3. Bottom line... there are many different ways to outline object for clipping paths (coined term for cutting out images from background in which images are save as .EPS with a vector path that defines the border of the image for use in other graphic programs) in Photoshop... which way you go about it depends on version of Photoshop, the actual image and its contents, and where or how the image will be used.
