The images in this post were created using a layer set to half tone in layer b blending options. Other effects have been achieved by experimenting with different blending options such as hard light, exclusion and saturation.
These functions were also used to create some further psychedelic effects:
image > adjustments > posterize
image > adjustments > hue saturaion
The following links have tutorials for working with halftone effects to get that retro, pop art look:
2. a more artistic look for halftoning:http://www.photoshopsupport.com/tutorials/cb/halftone.html
3. combined halftone screening with some other effects:http://www.photoshoplab.com/halftone-mania.html