I also have more CDs than I have space for (hasn't everybody?). I got a load of boxes from Ikea - they only cost a couple of quid each (or less). They're made of some sort of tough fibreboard and are self assembly - they come flat (apart from the lid, which is pre-assembled), and you fold them into shape and bolt them together with the bolts/nuts provided. All the holes are pre-drilled and the folds are already there, so it's dead easy even for the DIY-challenged.

They are really sturdy (they'e not just cardboard but a much stronger type of board), and come with a lid that has steel reinforced corners. They also have inserts on the end so you can label them with cards (all the parts are provided). They are tall enough so the CDs can stand edgeways up so you can read the titles (warning: check before you buy similar ones - I got some cheap ones from one of those 'pound' shops, and found the CDs have to go in sideways, so you can't see what they are without taking them out).

I put them on shelves with the ends facing outwards, so I can get more CDs on the shelves than I would if I just put the CDs on side by side. You can stack them, no problem, although I've never stacked more than 3 at a time.

The only drawback is that you have to open the boxes to see the CDs, but I don't fing that a problem. You can obviously sort your CDs into some sort of order to suit yourself, and label the boxes to make it easy to find a particular CD.

I also have some purpose-made CD shelves that match the bookshelves, also from Ikea (there was just space for these at the end of the bookshelves) and I tend to put my current favourite CDs in that, so they're easy to grab.

I forgot to say, they come in various colours, so you can colour-code your CD collection if you want! :-)

(No connection with Ikea btw, although it must sound like I am - I'm just happy with these particular boxes which I find very practical for the purpose).

HTH