HCP Inc. (DOC 1.21%)National Grid (NGG 1.50%) and Procter & Gamble (PG 0.60%) have what it takes to make them solid additions to retirement portfolios. They provide a nice combination of dividend-friendly cash flow and market-leading dividend yields, and each has reasons they could enjoy future bottom-line growth with less volatility than the broader stock market. If you're looking for promising dividend stocks for your income portfolio, these stocks are a good place to start your search.

Betting on aging baby boomers

Todd Campbell (HCP Inc.): If you're looking for a perfect income stock to tuck into your retirement portfolio, HCP Inc. might do nicely. The company is a real estate investment trust (REIT) that owns senior housing properties, medical office buildings, and life science buildings. With aging baby boomers boosting demand, HCP should be able to return plenty of money to investors via dividends over the coming decade.

A senior couple dancing on the beach.

IMAGE SOURCE: GETTY IMAGES.

Recently, HCP divested its struggling skilled-nursing assets to focus on core assets, and as fellow Fool Matthew Frankel pointed out, this allowed management to pay off debt set to mature prior to 2019, giving it more financial wiggle room to do deals.

Senior housing makes up 44% of HCP Inc.'s portfolio, and while rents generate a lot of its revenue, it gets about 40% of its top line from partnerships with big players in senior housing, including Brookdale Senior Living. About 22% of its portfolio is medical office buildings, and about 2% is life sciences buildings. As you can see in the following chart, this balance has allowed the company to steadily increase its dividend payments.

HCP Dividends Paid (TTM) Chart

HCP Dividends Paid (TTM) data by YCharts.

In the future, the company thinks it has billions of dollars worth of deals it can do that can grow funds from operations (FFO). Ultimately, that's good news for its dividend yield, which, by the way, is already a very respectable and retirement friendly 4.7%.

Strong dividends -- plus a special dividend kicker

Rich Smith (National Grid): Investors seeking dividend stocks for retirement can't go too wrong investing in the utilities sector. By definition, a utility stock is a stable business -- probably even a monopoly in the region where it operates -- and it's so insulated from competition that the government usually needs to regulate it to rein it in.

That's the kind of strong business I want to own, and National Grid is a great example of why you should consider investing in utilities, too. Priced at just 16.2 times forward earnings and paying a 4.7% dividend yield, National Grid makes money selling natural gas and electricity to customers in the U.S. and U.K., two developed markets whose growing need for energy won't be going away any time soon.

You may have noticed that National Grid's forward P/E ratio is a whole lot higher than its trailing P/E ratio -- currently just 4.7. There's a good reason for that. Earlier this year, National Grid sold a 61% interest in its U.K. gas distribution business to a consortium led by Australian investment bank Macquarie. This sale, valued at $17.8 billion, yielded a $7.5 billion profit for National Grid, dramatically inflating the company's trailing earnings and depressing its trailing P/E. (A further profit may be expected if and when National Grid succeeds in securing the sale of a further 14% interest in the gas unit to this same consortium).

What this means for dividend investors is that they can expect to receive a $5.42-per share special dividend paid out of cash generated from the sale -- and potentially, further special dividends if the secondary sale occurs -- on top of National Grid's already generous 4.7% yield. Additionally, going forward, National Grid has begun spending more than $1 billion on share buybacks, which should support the stock's price even as it reduces the share count and boosts earnings per share -- which could, in turn, permit higher, more regular dividend payouts in the future.

For investors who love dividends, it doesn't get much better than this.

Benefit from 60 years of dividend increases

Dan Caplinger (Procter & Gamble): Retirement investors like dividend stocks for their combination of income and growth, but one thing that they need from a stock is reliability in making dividend payments year in and year out. That's where Procter & Gamble shines, because the consumer-products giant has boosted its annual dividend every single year for more than 60 consecutive years. The company's 3% dividend increase that it first paid last month helped keep the stock's yield above 3%, and further demonstrated P&G's commitment to returning capital to shareholders.

Yet despite a recent slump in sales growth, Procter & Gamble has more going for it than just a good dividend yield. The consumer giant has recently gone through a substantial internal review to identify its strongest brands and make sure that it's dedicating enough resources toward building those brands. By jettisoning non-core businesses, P&G can increase productivity, and combined with gains in internal efficiency and cost reductions, the resulting boost to the bottom line can drive further share-price gains.

P&G's size makes it hard to produce the same growth rates that smaller rivals can achieve. However, for those with realistic expectations, Procter & Gamble has the ability to contribute both income and growth to retirement portfolios for years to come.