The German scientist Helmut Haas wrote that when two identical signals, each played through a separate speaker, are delayed by anything from 1-30ms, a sense of a broadening of the primary sound source is heard, but without there being a perceptible echo. This effect, often referred to as the 'Haas effect', can be created using delay plug-ins or track offsets, and can be used to add stereo width to a sound. 
The simplest way to use the Haas Effect is to add a delay plug-in to a track and increase the right output channel's delay time to 10ms more than the left. You should notice that rather than creating an echo, this short delay offset will make the track feel 'wider', thereby introducing a stereo spatialization effect.
Another approach is to duplicate a track, hard pan the original left and the duplicate right, then apply a delay to one of the tracks. If your DAW has the capability to set a track delay, you may use it to accomplish this. Otherwise, use a simple delay plugin that has a small (e.g. 10ms) delay, a 100% wet signal, and 0 feedback.
Unfortunately, this approach can create problematic side-effects. First, simply delaying one side in relation to the other will result in unpleasant comb filtering when the left and right channels are summed to mono. Therefore, this sort of processing can be risky if you want to ensure mono compatibility. 
A second problem with this treatment is that you can perceive that the undelayed side as louder than the delayed side, causing potential balance problems. 
To take advantage of the widening effect the Haas delays offer while avoiding the mono-compatibility trap, try adding a small amount of pitch-shifting to the left and right channels. To achieve this effect:
1. Set a mono delay to 11ms and with zero feedback, then pan it hard right.
2. Then, add a pitch-shift plug-in to take it up seven cents. Repeat this with a second delay, but this time pan it hard left, and pitch-shift it down by seven cents.
Alternative: Ping-Pong Delay
Very short ping-pong delays (e.g. 30ms) can also make excellent wideners. The output of the ping delay can also be polarity inverted before going into the pong delay. This technique is great for transparent widening and has excellent mono compatibility.