The Nintendo 3DS is a glasses-free 3D gaming portable due next February for ¥25,000 (US$299). That's a long ways away! Let's make a low budget version right now.
First you'll need a Nintendo DS, DS Lite, DSi or DSi XL. Take your pick! Next?
Next you'll a lenticular lens sheet. Then? Then, you'll need tape.
Cut a portion of the lenticular lens sheet to cover the screen of the DS. Affix it to the portable with tape. Enjoy glasses-free "3D"! If you cannot procure a lenitcular lens sheet, then you can always make this:
The lenitcular lens DS was spotted by Tokyo Tek at the MAKE: Tokyo Meeting.