What do Lemsip, Nurofen, Cillit Bang and Durex have in common? That’s right, they’re all made by Reckitt Benckiser (LSE: RB), as are Dettol, Gaviscon, Scholl and a whole host of other household names.

And those are just some that are well-known in the UK. Reckitt Benckiser does more than 90% of its business overseas, with the US market contributing around 25% of its annual turnover. That looks like a pretty safe company to me, and a defensive foundation is something a long-term ISA really needs.

Reckitt Benckiser pays very reliable, if unspectacular, dividends yielding a little over 2% per year. But on top of that, the shares have been making steady progress, with today’s price representing a gain of 11% over one year, 40% over two years, and 114% over five years.

On a P/E in the low-20s, the shares are on a higher rating than the FTSE average of around 14, but safety is usually rewarded with higher valuations. And over the next 10 or 20 years or so I see Reckitt Benckiser continuing to reward its shareholders.

Buy Oil?

While getting your timing right really isn’t of key importance for ISA investing, it can be a nice bonus if you happen to pick a low point — and I reckon the case for investing in Royal Dutch Shell (LSE: RDSB) is looking better by the minute. Regardless of the oil price, an investment in one of the big oil producers is likely to serve you well for decades. But now that oil has been looking relatively buoyant for more than a month and is edging up above $40 a barrel, I think the cake could be getting iced.

Shell’s expected dividend yields of around 7.5% won’t be covered by forecast earnings until 2017, but with rival BP having pledged to keep paying its own cash, Shell will be keen to keep it going too — and an oil price recovery is making that look more likely. Oh, and Shell operates a scrip dividend scheme too, so you can take more shares each year instead of cash, and that’s perfect for compounding your rewards.

On top of that, there’s a very strong buy consensus out there among the City’s brokers, and though they might often talk rubbish, I’m with them on this one.

Nicely diverse

Diversification can be key to ISA success, and adding pharmaceuticals giant AstraZeneca (LSE: AZN) would make up a nicely diversified trio. But more important than that, it’s a great long-term investment in its own right.

The company, along with rival GlaxoSmithKline, is still recovering from the expiry a few years ago of some key drug patents and increasing competition from generic products. But the strategy put in place by new boss Pascal Soriot is bearing fruit, and earnings per share could well pass their low point in 2017.

Forecasts put the shares on a forward P/E of 14 at today’s price of 3,900p, and if that’s all it can command at the bottom of an earnings cycle, then it will surely be looking like a screaming bargain once we see a return to growth. Meanwhile, reasonably covered dividend yields of 5% per year should keep investors ticking along quite nicely.

Whether you go for these three or not, a nicely diversified ISA could set you on your way to a cool million through investing in shares. But you don't need to take my word for it, you can get yourself a copy of The Motley Fool's 10 Steps To Making A Million In The Market report. It takes you through all you need to know, one step at a time.

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Alan Oscroft has no position in any shares mentioned. The Motley Fool UK has recommended AstraZeneca, GlaxoSmithKline, Reckitt Benckiser, and Royal Dutch Shell. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.