Not USA, but if you have a KBC in your country (a Belgian bank, but you'll find them in other EU countries) they offer a quite easy way to start investing in index funds.

Essentially, each time you use your debit card, they round up the amount you owe the shop, and put that in a special account. For each 10 euro in that account - they invest it.

So for example, let's say I go to the shops and pay 9.30 for groceries. Then I'd end up paying 10 euro to the shop, and 70c will go to the investment account. Once the investment account reached a multiple of 10 - it gets invested.

It's a way to slowly build up owning more funds.

Of course, you can also just put X euro in it to start of instead of waiting for the initial 10 euro. :P

edit: typos