GMail and GCal are wickedly powerful as is… but you can get some extra goodies and extra features via their “Labs”. To access these features in Gmail or GCal click the green beaker icon next to “Settings” in the top right hand corner of the page.

Background Send (GMail – Definitely Enable)

Background Send is one of the slicks features Google has baked into GMail; it lets you continue on working while Gmail sends mail in the background. If it fails, it will simply let you know and prompt you to try sending it again. This should be enabled by default and you definitely want it as it enabled. GMail is already fast but with this enabled it allows it to perform more like desktop client than a web application.

Undo Send (GMail – Definitely Enable)

Undo Send AKA “oh shit I didn’t mean to send that yet”. After sending an email, Gmail will wait a predefined number of seconds (5, 10, 20, or 30, configurable in Gmail’s settings) before sending—at any point during which you can hit the “undo” button to take back your mistake.

Nested Labels (GMail – Definitely Enable)

I remember when the power of “labels” versus folders really jumped out at me, it changed the way I looked at email… but it was so… FLAT. It used to require browser extensions to pull the ability to nest labels within one another. Labels are incredibly useful for organizing your messages, but there comes a point where you have so many that you need to organize your labels. Nested Labels is a great little feature that lets you create labels in a hierarchy—for example, separating mail into “work” and “personal”, and then further separating the personal category into “family” and “friends”.

Next Meeting (GCal – Definitely Enable)

Here’s another feature that should just be enabled by default. Next Meeting is probably the single most useful experimental feature in Calendar, because it shows you exactly what event is coming up next, along with a clearly readable countdown timer so you don’t miss it. It shows up as a widget in the sidebar, and the event displayed in the widget is highlighted the same color as the calendar set that it came from.

Inserting Images (GMail – Definitely Enable)

Plain text doesn’t always cut it.. In those situations, the Inserting Images lab will help you out by letting you insert images easily—whether you upload them from your computer or link to an external source on the net—with the press of a button. If you’re running Google Chrome or Safari, you don’t need this lab enabled—you can just drag and drop images right into the Gmail window instead.

Quick Links (Gmail)

Quick Links adds a small box to Gmail’s sidebar that lets you can add one-click access to any bookmarkable URL in Gmail. This can be —like saved searches, specific messages, labels, or anything else.

Multiple Inboxes (Gmail)

This is still one of LifeHacker’s favorite Gmail features, and with good reason, there’s a lot you can do with it. Whether you want to turn Gmail into your ultimate GTD inbox, use Gmail as your central, universal communications hub, or just manage multiple addresses (my preference), Multiple Inboxes has you covered by letting you stack extra lists of emails—whether they be labels, starred messages, or any other Gmail search—in your main inbox window.

Advanced IMAP Controls (Gmail)

If you like Gmail but use a separate mail client like Outlook or Thunderbird to access it, you’ve probably had some confusion with Gmail’s IMAP implementation. GMail is not and does not work like mail clients of the past. Labels are now folders-ish. Because you can multi-label messages you can have multiple copies of messages everywhere. If you access Gmail via IMAP, you’ll definitely want to enable Advanced IMAP controls, which let you select which labels actually show up in your mail client. Once enabled, you can access its settings from the Labels tab of Gmail’s settings. Personally, I ditched mail clients long ago and prefer to just work within GMail but if you’re still giving your thick client some love then you’ll want this turned on.

SmartLabels (Gmail)

Gmail’s Priority Inbox is pretty slick and good at telling you which messages are important. That said,  your “unimportant” messages can still be overwhelming. I’ve had my own labels setup for a while now, but now Gmail’s SmartLabels Lab can keep common types of messages—like bulk mail, Facebook notifications, etc. labeled and organized in your inbox. It will automagically detect which messages are bulk mailings, which ones are auto-generated, or sent from mailing lists or groups and label them all accordingly. This means you don’t have to keep up those filters yourself. If you don’t consider these messages spam, but still want to keep them separate from your other daily emails, this is a great lab to have around.

Unread Message Icon (Gmail)

It took forever but Google has finally implemented unread counts into the Gmail favicon. After enabling Unread Message Icon in labs, any Gmail tab you have open should show the number of unread messages in its favicon, so you’ll see whenever you have a new message. This is useful if you’re a zero unread inbox warrior but not so much if you like to keep things you intend on coming back to at a later time marked as unread.

Preview External Services in Messages (Gmail)

Gmail has quite a few labs that let you preview things like videos, documents, voicemails, and images in emails if they’re sent from certain services. For example, if one of your contacts sends you a link to a Google Doc, the Google Docs Preview Lab will show a preview of it right in the email. Not only does it you preview shared Google Docs, but it also lets you view any Google Docs compatible format before downloading it. That means the next time someone sends you a Word document, Excel spreadsheet, or PDF and you don’t want to download it and open it up in Office (or you can just ditch having Office installed at all), you can see what’s inside just by viewing its Google Docs preview.

Similarly, if someone sends you a message with an address in it, the Google Maps Preview Lab will automatically show you that address on a map. There are also preview Labs for Google Voice, Yelp, Picasa, and Flickr if you or your contacts use those services.

Apps Search (Gmail)

If you use Google Docs or Google Sites, Apps Search is a great Lab that extends Gmail’s search capabilities to those two apps. That way, when you search for something in Gmail, it’ll also bring up matching search results from Docs and Sites below the Gmail ones. If you’re a heavy Docs user, you’ll probably want to check out the Create a Document and Docs Gadget Labs.

Video Chat Enhancements (Gmail)

Skype is awesome, but Google Chat is baked into my default mail client, and the Video Chat Enhancements Lab makes it even more awesome. This lab adds the latest and greatest features to Google Video Chat like higher resolution and bigger windows.

Jump to Date (GCal)

This feature allows you to quickly jump straight to any date in the past or future, without a flux capacitor. Not only is it great for jumping back to check what events happened on past dates, but enabling it along with the Year View feature (below) is a great way to get a handle on long-term planning.

Dim Future Repeating Events (GCal)

This feature only applies to events that are slated for a specific time period, not a whole day. If there are recurring events scheduled for the same day they’ll dim slightly to make the slightly more important event stand out. Even though Google has opened up GTasks API’s I still find myself “scheduling” to do items in GCal… if it’s a recurring reminder this makes viewing your actual availability easier.