My fiance and I each picked out a name before we even met our piggies. I chose Dibbler because it's a character from a book series I love (Terry Pratchett), and I also thought it would sound adorable attached to a little guinea (It does!).
Fiance chose the name Ganon from the villain from the Legend of Zelda videogame series because he can turn into a giant pig. When we got them, we each chose one and gave them our name. And boy do they fit! Dibbler is an adorable little bubbly ball of fluff who wants to explore everything. And Ganon...well, Ganon's kind of a jerk (love him so!), so the villain name stuck more than we thought! We've taken to calling him King Ganon, because he's the only one who can figure out how to get onto the ledge in their cage, so we call it his throne.
Fiance picked out Ganon's name pretty easily, only mulling over a few others. I went through a whole list that I had to narrow down! I had a list of book characters, and a list of girl names if we decided on female piggies. Dibbler was almost Wicket, or Dart (short for D'Artagnan), Binky, and even after deciding on one I almost changed it to Tater Tot on the ride home!
Like other's have said, make a list and narrow it down from there. Looking back, nothing would have suited Dibbler quite as well, and it was the one that stuck out by the end of the week.