Another option, one that Patrick once asked about is the SilverStone CS-01HS. 6x2.5" HS with mITX support (vertical alignment, might be good for airflow). It is spendy though.
SilverStone Technology Co., Ltd.- CS01-HS
Edit: Ooops, missed that you're looking for picoPSU. The CS-01HS is SFX form...