For a long time, DS's ringtone on my phone was "Handlebars" by Flobots, because it was our first karaoke duet. He said he didn't want it to be his ringtone because it ends in nuclear holocaust... he preferred "Space Oddity," because that's got SUCH a happy ending. :p I just switched it to the Shiny Toy Guns cover of "Major Tom (Coming Home)," which I told him will have to be close enough.
My default ringtone right now is "Rock Star" by Miley Cyrus--I have no shame. :p For my sisters, I have "Short Skirt/Long Jacket" & "Yellow Submarine" (one is a huge Beatles fan), & for my parents, "Synchronicity II" (my mom is a HUGE Sting fan). My childhood best friend is "Fascination" by La Roux, & my best friend is "July, July!" by the Decemberists.
I use mobile17.com to clip ringtones, btw--they work for almost any phone and provider, & they're free. Let me know if you want me to invite you to use it--I get "points" if other people join that I can use to get my ringtones w/o a wait!