I don't use Scottrade, so I'm not entirely sure what their fees are. I know that Fidelity lets you buy just about any mutual fund you could possibly want, but they charge you a $75 handling fee to do it for you, and another $75 fee when you sell. At that point, it's easier to just transfer the money directly to the fund family where you want to buy the funds and pay no fees.

The thing that you might want to investigate are "exchange traded funds" (ETFs). Vanguard has a bunch of them ("VIPERS") as do a few other firms (iShares being one notable example). You buy and sell shares of an ETF in precisely the same way you buy and sell shares of a stock, paying the same fees, and so forth. For example, if you wanted to get some exposure to emerging markets, you might buy shares of VWO.

This recent Wall Street Journal article talks about how Vanguard's fees are much cheaper, which is a big plus for them.