Here is the definitive post on this subject. Feel free to stickie
Buck 110 ,I still don't have one yet though
A fully serrated Spyderco and a PE one (I have a Serrated SS Police and a Chinook3)
Americans need a Bowie and Brits need a Kukuri. As a Canadian and knife addict I feel the need for both.
A first rate custom from a top notch maker. I only have one custom but it is a Lambert Whar with CF scales and timascus bolsters and it is shockingly good.
A knife with history. I have a Second Pattern FS Dagger but what you need will be based on your interest and heritage.
Something for fighting zombies. I have a Cheness katana with custom wrap.
A slip joint
A first Rate military style folder like an Emerson or Strider
A SAK
A bunch of Moras and opinels etc as users
Some type of camping/bushcraft knife. Not necessarily an actual bushcrafter but something to make fuzz sticks etc. I have a Scrapyard SS4
A first rate neck knife like a Buck Hartsook or Atwood. I have a Strider ED.
The most important knife should be your EDC. It makes sense that the knife you carry every day should be one you feel strongly about. Mine is always changing currently a Swamp Warden