Today I’m looking at three FTSE 100 giants offering irresistible bang for your buck.

A mighty medical pick

Make no mistake: the long-running battle between ‘big pharma’ and generic competitors in key treatment areas still has some distance to run.

Indeed, industry giant AstraZeneca (LSE: AZN) has seen earnings drop during the past four years as revenues pressure has mounted. And further declines are predicted for 2016 and 2017 as labels like Crestor and Nexium come under attack from new market entrants.

Still, I believe investors should give AstraZeneca serious attention as its revamped R&D operations should get sales chugging higher again. The company chucked $5.6bn at drug development last year alone, 40% of which was thrown towards the rapidly-expanding oncology arena.

Meanwhile, the prospect of further acquisitions in hot growth areas gives AstraZeneca’s long-term sales outlook further fuel.

Consequently I reckon a prospective P/E rating of 13.9 times is a great level to latch on to AstraZeneca’s improving earnings opportunities. Furthermore, a predicted dividend of 280 US cents per share through to next year — yielding a handsome 5% — also represents tremendous value.

Manufacturing marvel

Like AstraZeneca, car-and-plane-parts manufacturer GKN (LSE: GKN) has also endured a rocky ride over the past year.

Fears over cooling Chinese car demand, slowing sales of civil aeroplanes, and concerns over the fallout of the Volkswagen emissions scandal have all whacked investor appetite for GKN.

But while the firm’s key markets may endure some short-term turbulence, I’m convinced the surging transportation needs of a growing, richer global population should drive demand for GKN’s technology in the years ahead.

The Redditch firm is expected to print a 2% earnings dip this year, before staging a 9% rebound in 2017. These figures produce P/E ratings of just 10.3 times and 9.7 times, respectively. On top of this, predicted dividends of 9.2p per share for 2016 and 9.7p for 2017 yield a handy 3.1% and 3.3%.

A financial favourite

Supported by bulging insurance product demand the world over, I believe Aviva (LSE: AV) should also prove a lucrative stock selection for sage investors.

Bubbly business flows show that the insurer is an expert when it comes to developing market-leading products in line with changing consumer and regulatory requirements. And the firm isn’t afraid to splash the cash to boost its presence in key territories, a point underlined by the acquisition of Canada’s RBC General Insurance Company for £281m in January.

The number crunchers expect earnings at Aviva to detonate in the years ahead — indeed, growth of 108% and 11% is pencilled-in for 2016 and 2017 alone. These projections create mega-low P/E ratios of 9.7 times and 8.9 times, respectively, while sub-1 PEG readings through this period underline the firm’s exceptional value.

And Aviva’s steady capital build is expected to result in dividends of 24.2p per share for 2016 and 27.8p for next year. These numbers create market-busting yields of 5% and 5.7%.

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Royston Wild has no position in any shares mentioned. The Motley Fool UK owns shares of GKN. The Motley Fool UK has recommended AstraZeneca. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.