MDLP, or MiniDisc Long Play, is a recent addition (it was introduced on the Sony MZ-R900 in 2000) to the MD feature list that increases the amount of music that can be stored on a MiniDisc. MDLP uses the newly-developed ATRAC3 codec at lower bitrates (132kbps and 66kbps for LP2 and LP4 respectively) than normal MD recordings (which uses ATRAC1, a different encoder). Sound quality is said to be comparable to MP3 at equivalent bitrates (I haven't received my Sony MZ-N1 so I can't comment personally).

The list of recorders and players that can read/write MDLP tracks is growing all the time. Here is a list of all the players/recorders that can read/write MDLP tracks in alphabetical order.

CD/MD Deck Recorders:

  • Marantz CM6200
  • Onkyo FR-V77
  • Sony MXD-D40
  • Sony MXD-D5C

Portable Players:

  • Aiwa AM-HX100
  • Aiwa AM-HX150
  • Aiwa AM-HX200
  • Aiwa AM-HX300
  • Aiwa AM-HX400
  • JVC XM-P2000
  • JVC XM-PX50
  • JVC XM-PX501
  • JVC XM-PX601
  • JVC XM-PX70
  • JVC XM-ZX5
  • Kenwood DMC-M55
  • Kenwood DMC-P33
  • Kenwood DMC-P55
  • Panasonic SJ-MJ10
  • Panasonic SJ-MJ50
  • Panasonic SJ-MJ78
  • Panasonic SJ-MJ90
  • Sharp MD-ST70
  • Sharp MD-ST77
  • Sharp MD-ST700
  • Sharp MD-ST770
  • Sharp MD-ST800
  • Sharp MD-ST880
  • Sony MZ-E500
  • Sony MZ-E501
  • Sony MZ-E600
  • Sony MZ-E606W
  • Sony MZ-E700
  • Sony MZ-E707
  • Sony MZ-E900
  • Sony MZ-E909

Portable Recorders:

  • Aiwa AM-F90 (clone of Sony MZ-R900)
  • JVC XM-R700
  • Kenwood DMC-M7R
  • Panasonic SJ-MR200
  • Panasonic SJ-MR220
  • Panasonic SJ-MR250
  • Sharp IM-MT880
  • Sharp MD-MT170
  • Sharp MD-MT180
  • Sharp MD-MT190
  • Sharp MD-MT200
  • Sharp MD-MT77
  • Sharp MD-MT770
  • Sharp MD-MT877
  • Sharp MD-MT88
  • Sharp MD-MT888
  • Sharp MD-MT89
  • Sharp MD-MT90
  • Sony MZ-B100
  • Sony MZ-G750
  • Sony MZ-G755
  • Sony MZ-N505
  • Sony MZ-N707
  • Sony MZ-N1 (first portable recorder with NetMD)
  • Sony MZ-R500
  • Sony MZ-R501
  • Sony MZ-R700
  • Sony MZ-R701
  • Sony MZ-R900 (first portable recorder with MDLP)
  • Sony MZ-R909 (first portable recorder with ATRAC1 Type-R DSP)
  • Sony MZ-R910
  • Sony MZ-S1 (first "Sports" portable recorder)

Deck Recorders:

  • Sony MDS-JA333S
  • Sony MDS-JB940
  • Sony MDS-JE440
  • Sony MDS-JE470
  • Sony MDS-JE480
  • Sony MDS-JE640
  • Sony MDS-JE770
  • Sony MDS-JE780
  • Sony MDS-JB980 (first deck recorder with ATRAC1 Type-S DSP)
  • Sony MDS-LSA1
  • Sony MDS-NT1 (first deck recorder with NetMD)
  • Sony MDS-PC3
  • Sony MDS-S50

Sources:
Minidisc.org - http://www.minidisc.org