I'd always go for 3M products! They do picture hanging strips that look exactly like Velcro but you stick one on the walk and the other on the frame. Looks great, doesn't move, put them on any wall. Job done! Most DIY places have a selection
I bought a cheap set of photo hooks from tesco years ago, I've seen similar things in B&Q and Ikea. It had loads of little nails and photo hooks in, as well as some wire and some little screw in rings, which I've used on two frames that had nothing to hand them by. I just screwed the little rings into the back of the frame on either side, threaded the wire through and twisted it round itself lots. Voila, hanging frame.
I'll have a google, see if I can find some links for the set I bought.