You can help yourself by reading Hasbro Annual Reports for the past few years. This is from memory, so I could be off a bit. They do mention that for WOTC (as others have said above) it was Magic the Gathering and Pokemon that was the true money maker for Hasbro for many years. D&D is not a big item for them. The reports from 2000-2003 go into detail about all the money they lost in WOTC former retail outlets that eventually were all closed.
Over the last two years, the minis have claimed the limelight in the stock report, as sales of Pokemon finally died off. I believe MtG sales are stable. At GENCON Dreamblade was very popular, but we won't know until Feb or March 2007 when they release 2006's annual report if the sales were significant to be noteworthy.
Charles Ryan last year, when he still worked for WOTC posted that their average hardback sold in the hundred of thousands. Be advised that retailers and distributors claim about 55%-60% of the retail price on the book. The printer and publisher get the reminder. IME WOTC collects around $9 on each $30 book, x 100,000 = $900,000. Not bad even if their developments costs are over $250,000 (my estimate) on each book (3-month development cycle I believe they use) and not including other overhead costs. It would not surprise if they weren't getting at least 20% net profit on each book. Though looking at the package sets of MM2, MM3, & FF and the Races set, not all the books have reached that level of sales. Seeing all the adventure modules for 2007, which primarily are aimed at DMs, its obvious they have re-thought they D&D book line for the forseeable future. Yet they have D&D other lines (minis) to carry them thru any dry spell IMO.
From the stock report the minis is making even more money for them, which is why the Star Wars went all mini last year - that's where the real money is. Which also keeps their distributors (who have more control than most of you realize) and retailers happy.
The movie line, (if I remember correctly) ties back to TSR's prior agreements with the studio. WOTC/Hasbro has little or no say in the matter, provided the Studio pays the yearly license fees. Despite the poor reception of the movie among the D&D faithful, the first one actually made money, which is why they made a second. If the second made movie, its likely the Studio will make another one.
I keep seeing talk of a Dragonlance series, but nothing out yet.
WOTC/Hasbro collects license fees from licensing out Dragonlance D20. Also it was collecting license fees from Ravenloft and Gamma World until the license holder finally gave up. I don't think they made as much money as they hoped on those two lines.
Dungeon's & Dragon's Online, not a WoW buster, but its still there and via license agreements with Atari, I am sure WOTC/Hasbro collects their license fees from Turbine's subscriptions.
Novels, art books, posters, etc. are other sources of income on the D&D brand.