your work is a mixed bag here - in some places you kind of miss the mark, with more unrefined work, and in other ares you absolutely nail it - I think the Megan Fox portrait is pretty nice.
The Sarah Michelle Gellar look-a-like - get rid of the giant M shade that goes around her nostrils and through the bridge of her nose. Make the eyes a tad bit narrower, and make them less white - they're too bright right now. Also, give those eye lashes some life (vary the strokes up a bit - eyelashes on top should be longer, eye lashes on the bottom usually not as long, not as pronounced) and there is always a line to define the top of the upper eyelid. Also, add some shading to the iris and the pupil. It'll make your work look MUCH more natural.
Your pencil works aren't bad either - I can't really tell if it's your style, or if you're having trouble with portraiture.. Quite frankly I think it's the latter option because your shading seems well done - you just get the features and spacing a little wonky. Likeness = achieved though, so well done!
Doctors heal you, Artists immortalize you.
"Those who can, do. Those who can't, teach" - bullshit.
The usual staples for anatomy: