John Bell (jbell) started (and I believe maintained) a list of pre-amps in a thread within this board; I am fairly certain a Search (of this sub-board) should yield the thread.
Quickly off the top of my head, and in no order; the Shure Mixpre clone, Denecke PS2, Naiant Littlebox, Naiant Tinybox, Acero MP2 (I think), Lunatec V2, Apogee Mini-Me, and Edirol UA5. There are a bunch more out there, those are the units that quickly jumped to mind.
It should also be noted, while all may not be battery powered, there are various means to power them with external batteries. For example, the Initial RB270 9v DVD battery.
HTH