Google Drive

Google Drive offers a free 5GB online storage. You can upload and access all of your files, including videos, photos, Google Docs, PDFs and beyond. Here is the URL

Google Drive

You can install Drive on your Mac or PC , and use the service via an app on your Android phone or tablet. Google also has plans for an iOS app in the future. Blind users can access Drive with a screen reader.
Google is offering all users 5GB of storage on the service for free. If you need more than the 5GB, then it is offering several tiers of storage options

Once you’ve shared content with someone else, you can add and reply to comments on anything (PDF, image, video file, etc.) and you’ll receive notifications when other people comment the items you’ve shared.

Here is a quick look at the pricing of similar products per month:

Service	Free storage	Cost for 25GB	Cost for 50GB
Apple iCloud	5GB	$3.33	$8.33
Box	5GB	$9.99	$19.99
Dropbox	2GB		$9.99
Google Drive	5GB	$2.49	$4.99 (100GB)
Microsoft SkyDrive	7GB	$0.83 (27GB)	$2.08 (52GB)

You can also upgrade to 1TB for $49.99/month. When you upgrade to a paid account, your Gmail account storage also expands to 25GB(Currently it is 10GB). You can attach photos from Drive to posts in Google+, and soon you’ll be able to attach stuff from Drive directly to emails in Gmail.

Facebook and Twitter from Gmail

Now you can use your Facebook and Twitter from your Gmail.
For enable this please follow below steps.

Go to Settings > Labs > enable "Add any gadget by URL"

After save changes, go again to Settings. you will see a new tab call"Gadgets"

Go to Settings > Gadgets > and copy below URL for Facebook and Twitter.

For Facebook: http://hosting.gmodules.com/ig/gadgets/file/104971404861070329537/facebook.xml
for Twitter: http://twittergadget.appspot.com/gadget-gmail.xml

After save changes you can go back to Gmail inbox.
now you will see Facebook and Twitter gadget top of invite a friend option.

For more gadget in Gmail, add below URL.
Wikipedia Search Gadget URL: http://www.google.com/ig/modules/wikipedia.xml 
Google Translate Gadget URL: http://www.google.com/ig/modules/dictionary.xml 
World Clock Gadget URL: http://gad.getpla.net/poly/clock.xml
Ask Word Gadget URL: http://www.openinventions.com/spellcheck/openinventions_spellcheck.xml
RTM Gadget URL: http://www.rememberthemilk.com/services/modules/googleig/rtm.xml 
Google Tasks Gadget URL: http://www.google.com/ig/modules/tasks.xml 
Google Calculator Gadget URL: http://calebegg.com/calc.xml 
Currency Converter Gadget URL: http://www.ac-markets.com/forex/currencyconverter.xml
Links To Google Services Gadget URL: http://blakewest.googlepages.com/googleservices.xml 

There are many other gadgets also that are use full and can be use in Gmail.