Depending on what you're looking for, there are a lot of ways to achieve harmony in an ecosystem of products and/or services. As JohnB said in a comment and as you note, Adobe Creative Suite and Microsoft Office are great examples:
An example that came to mind was the case where sports blogging network SB Nation redesigned their logos. Below is a sample, but I encourage you to visit the post to see how disconnected they all were before and how unified they look now:
Logos are kind of like Icons
Icons are a lot like logos in terms of the design process. With logos, you're trying to reduce a brand, an idea, a product into something that's simple, memorable, and flexible. With icons, it's a similar story. So when a commenter pointed out that the SB Nation logos reminded him of Foursquare badges, he makes a good connection.
Therefore, it might be worthwhile to check out some icons families, like this one designed by Susan Kare:
Here are some other icon examples that could inspire you.
An image on Wikimedia provides a nice infographic on the icon design process (Here's a link to the author Andaja's page...not sure which link will stick around longer.). I reference it for this particular part:
So, logos or icons that share a color palette, or a type of perspective, or a certain degree or method of abstraction will look more unified.
Identity is more than logos
Sometimes the logo stays the same, but a unified ecosystem can still be created by other means. XL Insurance is a great example:
Branding firm Wolff Olins did this for Staples and USA Today:
A final great example is when Nickelodeon rebranded. See how they went from logos that were pretty scattershot to a set of brands that were well-integrated:
You can't go wrong going to sites like Brand New and Wolff Olins to see how brands do it!