Epyx Fastload cartridge
Give you disk drive or SD2IEC device the boost it needs without having to open up the C64.
Comes with many built in DOS Wedge commands that make light work of opening and running disks.
Comes with a system reset button also.

Full manual can be found here

http://rr.c64.org/rrwiki/images/c/c4/Epyx_FastLoad_Manual.pdf