My bicycles are stored like Velogirl suggests. They hang by a wheel, from vinyl vovered bicycle hooks in joists of the basement ceiling. I alternate hanging by the front and rear wheels make more efficient use of space.
Some people do not like hanging from the front wheel as they feel this causes stress on the headset, While this is true, the stress has not been great enough to cause any problems with the headsets. Also, I have yet to have a front wheel disengage from the fork, causing the bicycle to fall to the floor. Potential for this problem is eliminated by hanging from the rear wheel, if it has horizontal dropouts, but if you use handlebars which are wider than the typical 16" (45cm) joist spacing, then you cannot hang one bicycle per joist.