15 Meter Moxon by AD5UQ
Well, I told you I'd give it a try, so here is my version of a Moxon antenna. I had some 3/4" PVC pipe for the spreaders and a piece of thick Plexiglas for the center support.
http://www.moxonantennaproject.com/ad5uq/AD5UQmoxon.htm

3 Half Wave 15 Meter Doublet (in phase) by KC8AON
For a good multiband ( 10 thru 40 meters ) antenna, try a 3 half waves in phase doublet for 15 meters.
It is derived by using the formula for the G5RV, but substituting 21 Mhz in place of the usual 14 Mhz.
http://diz.faithweb.com/builders/15mdub.htm

A Light and Sturdy Quad for 10 and 15 meters by KA3PDM & W3/CE3VU
Fishin' for DX? A few fishin' poles and a hank of wire can help you snag the Big One!
http://www.arrl.org/tis/info/pdf/9107030.pdf
 

A Small Transmitting Loop Antenna for 14MHz and 21MHz by VK5BR
By definition, the small transmitting loop has a circumference less than one quarter of a wavelength. Because of its small size, it is possibly an attractive proposition for someone with inadequate space to erect a larger aerial.
http://www4.tpgi.com.au/users/ldbutler/HFTXLoop.htm

The HF Satellite Antenna by W4SAT
This is a no compromise dual band antenna. Instead of using traps, this design interlaces two separate antennas on one boom. This is a full size, four element beam on 10, and three elements on 15 meters!
http://www.qsl.net/w4sat/hfsat.htm

The One Element V Beam! by KB4XJ
"I refer to this as my ONE ELEMENT BEAM, It's a horizontal Vee!" ...
In log-periodic dipoles, it was found that forward tilt increased gain by a 3 to 4 db over a regular log dipole.
http://www.hamuniverse.com/1elbeam.html