I am not so bold or conceited in my music nerddom to dare tell you what to put on your mix, so this is all you. You want some Hoobastank to go with your Toad the Wet Sprocket, go for it. Merzbow? Sure, it's your funeral. Maybe nothing says "I Love You" like a couple Anal Cunt songs… who knows?
No one wants a mix filled with sentimental tunes to come on a logo-filled Office Depot CD-R. In order to find your way into his/her pants you're going to need to put in some more effort, and don't even think of just taking a Sharpie to it. You're not Basquiat and that CD-R is not your canvas. Instead pick up some of the amazing pre-designed blank CD-Rs at 5inch (www.5inch.com). With a wide range of artwork styles, these are perfect for your sensitive indie mix, or that banging "Crunkastical 2005" mix you've been working on. 5inch's CDs look stylish enough to pass for the real thing, plus they have a clear bottom so they don't look like you burned it at home.
Now you have that sweet-looking CD, you're going to need something to put it in. Sure the standard jewel case might do the trick, but do you really want to enter a whole world of artwork templates and perforated tray card edges? Besides, after you break up, it's not like they're going to file the CD with their others. Keep it special by picking up some of the Arigato Pak! cardboard sleeves from Stumptown Printers (1115 SE Morrison). These natural sleeves are self-assembled and are a blank template for whatever artwork you deem fitting. Plus, they're a perfect fit for throwing in some extra items with the CD, like X-rated Polaroid photos of yourself. Or a zine or something. But, really, do the photo thing.