For diehard fans of Excel who have switch to Google Apps products, you need to try out the new Google Sheets!
Google just announced a significant upgrade in functionality, including support for offline editing and new filter views for simpler sharing.
For now, you will need to opt-in to use the new functionality. Turn on the new Sheets by checking the “Try the new Google Sheets” box in Google Drive settings. From then on, all new spreadsheets you create will work offline and include these new features. The post on Google's Office Blog mentions that Google will be adding a small list of missing features in the coming months. Note that the new functionality will only effect new sheets you create after opting-in.