daryn, everyone yaps about roth iras but you can't contribute if you make more than like 100k. they also work better if you'll be making more money later in life, which might not be the case for a lot of poker players. maybe a regular ira is worth looking into for retirement though.
money market bank accounts often suck. if they're not around 5% look into "no risk CDs". i hadn't heard of these either, but bank of america has 9 month CDs for around 5 points with no withdrawal limits or penalty.
fwiw i tend to just dump money into index funds, which are like stock market versions of mutual funds.
SPY is where i put the most, it simply tracks the s&p 500. i use
sharebuilder as my brokerage because they have easy automatic investment stuff (e.g. "take $X/month and split it among the following stocks"), allow ownership of partial shares (which makes fixed dollar amt investing easier), low fees, etc.