Since this is your emergency fund, you generally want to avoid volatility while keeping pace with inflation. You really shouldn't be looking for aggressive growth (which means taking on some risk). That comes from money outside of the emergency fund.
The simplest thing to do would be to shop around for a different savings account. There are some deals out there that are better than ING. Here is a good list.
The "traditional" places to keep an emergency fund are Money Market Mutual Funds (not to be confused with Money Market Accounts). They are considered extremely safe investments. However, the returns on such a fund is pretty low these days, often lower than a high-yield online savings account.
The next step up would be a bond fund (more volatility, slightly better return). Pick something that relies on Government bonds, not "high-yield" (junk) bonds or anything crazy like that.
Fidelity Four in One comes pretty close to your "index of indexes" request, but it isn't the most stable thing. You'd probably do better with a safer investment.