I don't have many beers I've actually named but there are three ways I name them.
Brew to the name: somebody had a thread going about stout names and somebody else replied black hole, my train of thought went to singularity, which seemed fitting for a belgian stout. Bottled it last week. I was reading something that mentioned Pax Romana. Being a big fan off [unhealthily obsessed with] the Principia Discordia, my brain [pineal gland] decided Pax Discordia would be a great name for an APA. It was September last year, I had a ton of Centennial, and it was hard to find before the 2012 harvest, so I went with it. Watching some old Southpark episodes I decided scuzzlebutt is a great name--imperial stout coming up in a few weeks.
Continue naming convention: None so far, but this weekend is the first. APA with the same target OG/FGs and IBUs as my Pax Discordia, but all Mosaic hops. Still not sure if I'm going with Pax Mosaic or Pax Mosaica. Mosiac sounds better to me but I kind of want to force that A at the end, but at that point I'll be stuck with an A at the end of any of my APA variations.
A tip of the hat: Pretty much for clone brews and "inspired by" brews. My apricot ale is Magick Cap #23 [bonus points if you get it--not the magic hat #9 part]. Last year I brewed tripel on April 1, I intended it to taste like Eau Benite and named it Eau D'Imbecile in a rough translation of Fool's Water. This April 1 I am going to brew a golden strong based on the PranQster info in BLAM, with harvested PranQster yeast (I know that it is two yeasts and the ratio has probably changed) that I plan on calling LoQi. Scuzzlebutt reminded me of Yeti, which is probably part of the reason I want it to be an imperial stout.
I only have one that was named based on the brew day. My first dubbel and my first night time brew, different boil off than I was used to, very windy outside, autosiphon stuck while transferring wort, put a giant splinter in my heel while brewing, finished higher than I would have liked. Named her Nemesis, she's delicious now but a bit sweeter than I hoped for.