The information you keep in Google apps like Gmail, GCal and Reader doesn't just live in one place. Check out a few easy but non-obvious ways to plug different Google apps together and share their data and features.
Get Your Calendar in Gmail
One of the most useful integrations available for Gmail and GCal users, the Google Calendar gadget puts upcoming events on your email sidebar. To turn it on, just enable the Google Calendar gadget in Gmail Labs. Click on the Options link to configure which calendars you want to display events from, and schedule events directly from Gmail using the gadget's Add link. (Gmail Labs offers lots of other app integrations, like YouTube previews in Gmail, the ability to create a Google Doc from an email conversation, Picasa image previews, Google Docs as well as a Google web search gadgets.)
Put Your Gmail Messages on Your Calendar
Gmail Tasks's killer feature is how it can act as a bridge between your email inbox and your calendar. If you add a Gmail message to your Tasks list (just choose "Add to Tasks" from the "More Actions" drop-down) and add a due date, that task shows up on your Google Calendar on that date. Even if Gmail's Tasks module isn't your primary to-do list app, this is an easy way to "schedule" email you don't need to deal with right now but does have a deadline in the future.
Get Google Docs in Your Calendar and Gmail
Courtesy of Google Calendar Labs, you can easily attach Google Docs to any event—like the batting lineup for the company softball game next week. In GCal's Labs area (in Settings), just enable the "Attach Google Docs" feature.
Gmail has had built-in integration with GDocs since back in 2006; any time you have a Word document or spreadsheet email attachment in a message, Gmail gives you a "Open as a Google Document" link next to it. You can also convert an entire Gmail conversation to a Google Doc by enabling the Gmail Labs' "Create a Document" feature.
Get Google Profile Feeds in Google Reader
Google's newish Profiles tool offers an interesting integration into Google Reader: the ability to associate people with the feeds they create. When you configure your Google Profile and enter the web sites where you've set up shop, the feeds available for those sites appear on your profile—as well as in Google Reader. When you're following someone in Google Reader, you can easily see their blog and social network feeds alongside their photo and bio thanks to Google Profiles. From the ever-so-specifically-labelled "Browse for Stuff" section in Google Reader, click on the "People You Follow" tab to browse the folks you care about and subscribe to feeds they're creating.
Get All Your Google Apps on iGoogle
You can't mention integrating Google apps without giving iGoogle a nod. GApps addicts' homepage of choice, iGoogle offers Gmail, Google Talk, Google Calendar, Google Docs, Gmail Tasks, and Google Voice gadgets for the ultimate, all-in-one, Google apps jumping-off spot. (In fact, last week during the Gmail outage, iGoogle's Gmail gadget was still working—even when the proper Gmail webapp was down.)
...Not to Mention Integration Add-ons and Your Browser Sidebar
Beyond in-webapp ways to access Google apps data across products, you can also hook up browser extensions like Integrated Gmail or iGoogleBar for Firefox. Alternately, for easy Google apps access no matter what web site you're on, put your browser's sidebar to good use.
What other ways do you use one Google app's data in another? Shout it out in the comments.
Gina Trapani, Lifehacker's founding editor, likes finding new ways Google Apps inform one another. Her feature Smarterware appears every week on Lifehacker.