Most of the friends I know use Gmail (or Google apps for domain) as their primary email client.
Google apps (Free) version come with 25 GB email storage for each user. You can upgrade to a higher version and add more storage.
If you are a Gmail users and already used or close to using all of 7GB+ space that comes with it – you need create an additional email account for your email. You can simply buy storage from Google. Additional storage comes real cheap. It starts at $5 USD per year for 20GB storage.
You can find details on Google Purchase storage page and buy additional storage. You need to be logged in to your Gmail account to see the details.
I have listed the price for easy viewing.
20 GB ($5.00 USD per year)
80 GB ($20.00 USD per year)
200 GB ($50.00 USD per year)
400 GB ($100.00 USD per year)
1 TB ($256.00 USD per year)
2 TB ($512.00 USD per year
4 TB ($1,024.00 USD per year)
8 TB ($2,048.00 USD per year)
16 TB ($4,096.00 USD per year)
This storage is not limited to Gmail only and is shared between Gmail, Picasa Web Albums, and Google Docs. Space you get is in addition to the free space provided by these services.