Merriam-Webster's Collegiate Dictionary:
mega-
megabar
megabit
megabuck
megabyte
megacity
megacorporation
megacycle
megadeal
megadeath
megadose
megafauna
megafaunal
megagamete
megagametophyte
megahertz
megahit
megakaryocyte
megakaryocytic
megal-
megalith
megalithic
megalo-
megaloblast
megaloblastic
megalomania
megalomaniac
megalomaniacal
megalomaniacally
megalomanic
megalopolis
megalopolitan
megamerger
megaparsec
megaphone
megaphonic
megapixel
megaplex
megaproject
megara
megarian
megaric
megascopic
megascopically
megasporangium
megaspore
megasporic
megasporogenesis
megasporophyll
megastar
megastardom
megaton
megatonnage
megavitamin
megavitamins
megawatt
meghalaya
meghna
megiddo
megillah
megilp
mego
megohm
megrim
meighen
meiji
meikle
meiny
meiosis
meiotic
meiotically
meir
meissen
meissen china
meissen ware
meissonier
meister
meistersinger
meitner
meitnerium
mek
meknes
mekong
melaka
melaleuca
melamine
melamine resin
melan-
melancholia
melancholiac
melancholic
melancholy
melanchthon
melanesia
melanesian
melanic
melanin
