Siliconera reports on the contents of the upcoming Kirby 20th Anniversary Compilation that is due out this July in Japan and hopefully later on in Europe:
Kirby's Dream Land (Game Boy)
Kirby's Adventure (NES)
Kirby's Dream Land 2 (Game Boy)
Kirby Super Star (SNES)
Kirby's Dream Land 3 (SNES)
Kirby 64: The Crystal Shards (N64)