Many months ago, I made a post about using ping-pong delay as a method of widening mono sounds. This can sound nice, but as one reader rightly pointed out, it only works well with certain types of sounds like pads since more percussive sounds make the delays themselves obvious.
A much older method of fattening up a mono sound with a stereo image is to make a copy of your mono track and delay that copy by a small amount. Of course you can do this manually, but Logic's Sample Delay plug-in does a pretty spiffy job of it too. This is a delay plug-in that has settings at the actual sample level instead of milliseconds.
Simply select the mono track you wish to widen, apply an instance of Sample Delay (make sure you select the Mono->Stereo version or you won't get any effect), and delay one of the channels. The higher the value, generally, the wider the effect. There is a point of diminishing returns, however, where the actual delay itself becomes apparent (although this can produce some cool John Lennon like vocal effects). Try anywhere between about 200-2500 samples to taste. The great part about this effect is that the shorter delay times allow you to widen percussive sounds like synth bass without the delays being perceptible.