many mutual fund companies let you get started with an automatic monthly investment of as little as $50 a month - you choose the mutual fund up front, and they automatically deduct the money from your checking acct each month on teh day you specify - TRowe Price, Vanguard and Fidelity are large mutual fund companies - with dozens of different kinds of mutual funds each to choose from - ONLY BUY "NO LOAD" funds - your entire $50 will be invested for you - no sales commission
You can always take a look into this site. I have an account with them myself and I have been putting away a small amount for the past 6 yrs..
http://home.ingdirect.com/