One of the most useful items I've crocheted is a hook case. It keeps all my hooks, stitch markers, needles, scissors, ruler, pencil, and whatnot organised. I got the pattern from http://www.sarahanns.com/crochetworks/case.html.
This was a very simple project done entirely with sc except for the flower and leaves which were also surprisingly easy to do. I did make one error, the pouch in the middle was supposed to have been sewn on lower, right near the bottom. The flap at the top was actually supposed to have been attached at the sides and just meet the top of the pouch rather than overlapping it. But I'm quite happy with it the way it is. I much prefer having a flap that is easily opened rather than an upper pouch as is called for in the design. If I did it again, I think I'd make the pouch taller so that it reached the bottom of the case but leave the flap the way it is.
Worsted weight yarn in grey
Worsted weight yarn in green
Moda Dea "Aerie" yarn in pink (oooh, it's so soft!)
Black wooden button
Pink plastic bead
Thread (the button hole was too small to use yarn)