Check out the The All Band Doublet and the NorCal Doublet for very simple, effective and versatile antennas for multi band operation:
The all band doublet antenna is nothing more than a 1/2 wave dipole cut for your lowest operating frequency and fed with twin lead, ladder line, open wire, etc to a tuner that will accept a balanced line connection. IT IS NOT FED WITH COAX!
It can be designed for use from 160 through to 10 meters very easily using the standard 1/2 wave dipole formula:
468/freq MHz = total length (ft)
The exact length is not critical!
If there is insufficient room for a lower frequency version (160m or 80m), then the double can be designed to the shorter wavelength of the 40 metre band and used up to the 10 metre band. (Do not attempt to operate on a lower frequency than 7 MHz in that case since this could damage the a.t.u.) It may be possible to connect the ends together and tune it against earth - if you have a good enough earth - and use lower frequency bands. For best results a doublet should be mounted as high as possible (as with many aerials) and can be erected as a flat top or inverted V.
For more see the dedicated page: The ALL Band HF Doublet on Ham Universe: http://www.hamuniverse.com/hfdoublet.html