LONDON -- Next week sees more FTSE 100 companies going ex-dividend. If you want to be eligible for a firm's payment, or if you're hoping the shares might drop disproportionately when the time has passed, you need to be aware of the crucial dates.

Here are three FTSE 100 companies going ex-dividend next Wednesday, April 24. None is offering a massive payment, but they're all on the rise.

Old Mutual (OMU -1.52%)
Old Mutual is set to go ex-dividend with respect to its final dividend. The payment of 5.25 pence per share was announced on March 1 and takes the life insurance company's total annual payout to 7 pence per share, which is 23% ahead of the 5 pence paid for 2011.

On the current share price of 199 pence, that represents a dividend yield of 3.5%. The latest forecasts suggest respective yields of 4% and 4.5% for the next two years, with the shares on a forward price-to-earnings ratio of 10.

Rexam (REX)
Packaging-maker Rexam goes ex-dividend on the same day, and again it's a final dividend. This time there's a payout of 10.2 pence per share due, lifting the full-year total by 6% to 15.2 pence -- the firm paid 14.4 pence per share in 2011.

With Rexam shares currently on a price of around 520 pence, that 15.2 pence dividend provides a yield of 2.9%. That doesn't reach the FTE 100 average of around 3.1%, but after the firm slashed its dividend in the crunch year of 2009, it has been steadily recovering -- and we have more growth forecast for this year and next.

Aggreko (AGK)
Aggreko, the supplier of power-generation and temperature-control equipment, is our third for today, also with a final ex-dividend date next Wednesday. Aggreko's payment of 15.63 pence takes its full-year payment to 23.91 pence per share for a 15% rise on 2011.

In terms of yield, that's a modest 1.3% based on today's share price of 1,791 pence, but Aggreko's dividend has been rising over the past few years. And though earnings are forecast to fall a little for 2013, there is still a further increase of 8% to 9% in the dividend currently forecast by the City.

Dividends like these can add nicely to your investment returns -- they can be spent or reinvested, according to your needs. Whether you're investing for income or growth, good old cash is always welcome. And that's why I recommend the brand-new Fool report "The Motley Fool's Top Income Share For 2013," in which our top analysts identify a share they believe will provide handsome dividend income for years to come. But it will only be available for a limited period, so click here to get your copy today.