TD AMERITRADE (Nasdaq: AMTD) is grabbing up assets like there's no tomorrow.

The company reported fourth-quarter and full-year earnings this morning and set a record for net new assets garnered. The discount broker collected a record $41.5 billion in net new assets for the year, including $12.4 billion in the latest quarter, representing a 12% annual growth rate.

Revenue for the fourth quarter rallied 15.5% up to $703.5 million, of which the company pocketed $163.7 million of net income, or $0.29 per share. For the fiscal year 2011, revenue came in at $2.8 billion and earnings per share of $1.11. As a result, AMERITRADE has decided to up its quarterly dividend by 20% up to $0.06.

Average client trades per day were roughly 416,000, driven by recent market volatility. Commissions accounted for 44.8% of quarterly revenue, far higher than rivals Charles Schwab (Nasdaq: SCHW) and E*TRADE Financial (Nasdaq: ETFC). The rest of the quarter's sales were driven by asset-based revenue sources like interest and other fees.

The tough interest rate environment continues to weigh on the sector by shrinking the spread that brokers earn on net interest income. Money market fee revenue dropped a whopping 65.7% to $1.2 million. AMERITRADE also waives money market fees to avoid negative yields, similar to Schwab's practice.

The company opened 150,000 new accounts during the quarter, and total funded accounts now sit just above 5.6 million. Total client assets totaled $378.7 billion at the end of the period, far less than Schwab's $1.6 trillion in client assets.

Discount brokers are one of the rare subsectors within financial services whose balance sheets aren't absurdly complex or excessively riddled with valuation models. The business is much more straightforward and easier to understand, and after all, buying what you know is the start to constructing a market-thumping portfolio.