Schwab has a largest variety of mutual fund offerings, mostly no-fee, and is a discount brokerage.
Fidelity offers no-fee and loaded funds. Since the question mentioned this, note that Morningstar selected Fidelity funds as three of their Top 5 ranked funds of 2011 (in a fixed-income category maybe? I don't recall). This was just announced a few days ago.
Vanguard is good too, certainly for index funds. However, Schwab or Fidelity are better if you're interested in funds with higher-risk profiles.
Consider E*Trade, for mutual funds and ETF's. There's a little variation, but as of today, E*Trade offers 7600 mutual funds!
Merrill is your broker. I assume you have a fee-based account. If you pay fees, you should get the widest range of fund alternatives to pick from! That is puzzling. I can't imagine why a full-service broker would have a smaller selection of funds than Schwab or Fidelity. A full-service broker should also be able to offer you specialty funds, e.g. those with higher risk, as you expressed an interest in, more easily.