Last year I wrote about iRingPro, a group dedicated to bringing "ringtones for adults" to the iPhone. At the time they had one set of 27 tones available simply called "Zen," and they really do sound good. In fact, I still use them today ("Tokyo Station - Hi" Is my favorite).
Most feature a series of unobtrusive tones followed by a brief pause. If you've ever been annoyed by the guy whose phone unexpectedly blasts "Enter Sandman," then the Zen tones are for you.
They've recently updated the Zen series to include longer pauses between tones. Additionally, they've introduced two new collections, "Origin" and "Tek." Each collection contains between 22 and 31 tones featuring brief silent pauses and another full set with extended silent pauses in either MP3, iPhone for Windows or iPhone for Mac format. I must admit that I'm quite tempted by the Origin pack.
It's true that you can make your own classy tones with GarageBand, but these sound great and won't embarrass you when your phone goes off at a PTA meeting. Each bundle costs $9.95. If you purchased the original Zen set and were wise enough to save your receipt, you can upgrade to Zen 2 for free.