In a Google search I just found an interesting antenna concept for simple antenna capable of running 4, 6 and 10m.
The antenna is essentially a 10m dipole (can be horizontal or vertical) fed by two lengths of twin-lead cable in series, (from the antenna feed point to the coax) 86cm 450ohm and 295cm 300ohm, fed directly (or via a 1:1 balun) into a 50ohm coax cable. The antenna in itself is 2 pieces of wire, each 258cm long (essentially a 10m dipole antenna). The antenna is a relative of the G5RV type, though not identical.
The gain on 10m is, of course 0dBd, on 6m the antenna probably has a gain of 1 - 1.5dBd, and on 4m it is an Extended double Zepp (2x5/8), and the expected gain is around 3dBd. Sounds to me like a neat compromise for a tri-band antenna.