I enjoy taking occasional power naps after lunch or in the afternoon. I rarely fall asleep, but when I do, it really is refreshing.
One tool I discovered are Binaural Beats:
A binaural beat is an auditory illusion perceived when two different pure-tone sine waves, both with frequencies lower than 1500 Hz, with less than a 40 Hz difference between them, are presented to a listener dichotically (one through each ear).
For example, if a 530 Hz pure tone is presented to a subject’s right ear, while a 520 Hz pure tone is presented to the subject’s left ear, the listener will perceive the auditory illusion of a third tone, in addition to the two pure-tones presented to each ear. The third sound is called a binaural beat.Wikipedia
Keep in mind that you need to set an alarm (for example for 15 or 30 minutes). Or else you might find yourself sleeping for 2 hours, disrupting your day and sleep schedule.