Yes there is, probably several vehicles, but one is the DRIP ... Dividend Reinvestment Program ... many companies have. You find a stock you like that has one one of these programs (Google it probably) and sign up for it. Some may have an initial deposit to buy 1 share of its stock, but after that, you can send in what you want, whenever you want. These are all dividend paying stocks so when dividends are paid, they are automatically reinvested.
Most company's, like H&R Block, and no fee or commission; others, like IBM, do (I am not recommending them, they are the last two I still have as I have changed the method I invest). I would pick the ones that don't charge commission.
I don't know if there are any good mutual funds that let you invest that little, but there may be. ING Direct Bank has a "Sharebuilder" plan that may fit your needs, although in looking them up, I noticed they got popped for a $600 million fine for transactions involving Iran.