ETrade allows this without fees (when investing into one of the No - Load / No - Fees funds from their list).
Not exact matches
Many popular brokers
allow for the re-investment of dividends (they often refer to the programs as DRIPs), such as
ETrade, Schwab and TradeKing.
Many trading platforms (
ETrade, that I use, for example)
allow investing on some of those as well.
Check with the various low cost brokerages such as
ETrade, Scottrade, and TDAmeritrade, to see what their policies are, and what if any funds / ETF's they
allow you to trade in without commissions.