Three of today's most actively traded large-cap stocks among the options crowd are Citigroup Inc. (NYSE:C - 42.01), Herbalife Ltd. (NYSE:HLF - 43.79), and Nokia Corporation (ADR) (NYSE:NOK - 4.61). Here's a quick look at some interesting activity in these option pits today.

Bank stock C is set to report earnings before the market opens this Thursday, Jan. 17, and it looks like one speculator is bracing for a big post-event move. Earlier today, three blocks totaling roughly 1,900 contracts traded near the ask price on C's January 2013 42-strike put, while three matching blocks simultaneously traded near the ask price at the equity's January 2013 42-strike call. In other words, it looks like this trader implemented a near-the-money straddle in hopes of profiting from a major post-earnings price swing.

Meanwhile, the most active HLF option this afternoon is the January 2013 40-strike put, where 5,064 contracts have crossed the tape. Implied volatility on this in-demand strike has surged 15 percentage points to 95.4%, coinciding with a rally of roughly 9% in the stock. Data from the International Securities Exchange (ISE) suggests today's volume at the January 40 put is a fairly even mix of buy-to-open and sell-to-open activity -- which means some traders think the beleaguered stock has found bottom, while others are still bracing for a deeper decline.

As for NOK, traders have set their sights on the security's February 5 call, where 7,477 contracts have changed hands. Implied volatility on the option is down 1.6 percentage points at last look, and ISE data suggests the majority of these out-of-the-money calls have been sold to open. By writing 5-strike calls on NOK, traders are looking for the shares to remain stuck below $5 through back-month expiration. However, the skeptics have been wrong on NOK lately, with the shares up nearly 70% over the past two months.

The 20 stocks below have attracted the highest options volume -- in the front three-months' series -- during the past two weeks. Data is courtesy of Schaeffer's Senior Quantitative Analyst Rocky White.