Screenshot courtesy of E*Trade
E*TRADE introduced their free BlackBerry trading app a while back. It is now joined by a free version for the iPhone…
E*TRADE Mobile Pro 1.0 (iTunes App Store)
The app requires, as you might expect, an E*Trade account and lets you manage your investments in that account from your iPhone. It provides real-time quotes with charts, financial market news, stock/options trading and cash transfers between E*Trade and another institution (presumably with prior authorization in place).
It has an impressive 4 star (out of 5) rating based on 1044 ratings.
E*TRADE Mobile Pro for iPhone (product page)