Try putting the main instrument in one channel while its delay is panned to the other side. Apply reverb to the delay for a ghostly kind of echo. You can also try adding regeneration to the delay so you get multiple echoes. Be careful, though. It's easy to get carried away and clutter the mix.
Some delay units allow high frequencies to be rolled off on repeats.
Another interesting effect is a ping-pong delay, where the repeating echoes alternate between the left and right channels as they decay. Use this sparingly, though. Generally multi-tap delays are used as a special effect, but when carefully applied they can be used to create a light ambience that almost sounds like reverb, yet allows more space for other instruments to sit in the mix. Though a slapback can tend to conjure images of Wolfman Jack and Happy Days, the effect stands on its own, creating a very specific type of tension and mood that's sometimes just the right touch in a recording. Multitap delays such as this plug-in from Power Technology offer multiple independently editable dlays.