Any will do. In fact if you listen to the HTC fellow who demoed the car dock and car mode for people at MWC (check this site and PocketNow), he mentioned that the Beats Audio enhancements work over Bluetooth to their dongle plugged into a car audio head unit. That's what makes it such a Big Deal that Beats now works for all music apps installed on the handset, not just the HTC music app.
Head to head-fi.org to research if the Beats earbuds are all they're hyped to be. Personally I think everyone's ears are different, so a single brand/model of IEMs are never going to be the ne plus ultra for all. Oh, it's delightful if your new phone comes with ~$90 earbuds included, but for some they'd just eBay those and use their $400 Monster Miles Davis Tribute buds instead. (Or custom-molded Etymotic or UE or....)
I still think the Beats partnership and marketing is a waste of money. The logo ruins the back cover. The tech is just a fancy equalizer setting. Not everyone likes the red accents, and in many cases they can't choose the classic colors. It costs money to implement it and to market it, and HTC is using it as an excuse to keep their phone prices sky high. I think its wholly unnecessary. But they have to milk it because people will go gaga over the Beats branding for some reason. If they wanted to add value, they would just stick it in all their phones and make it a standard part of HTC sense without all the hohum.
I plug in a pair a JVC flats and the music sounds brilliant. Ive never listened through any Beats earphones so cant comment, but if youve got some earphones you like already, they might sound better on the phone.