Gmail allows mail fetching from other email provides using POP3. This is available from 2006 in Gmail settings but I never had to use it before. Recently I added an office email ID to Gmail to better manage emails.
I noticed that Gmail fetches new email from the POP server at specified intervals only, typically every 60 min. I am looking for a script to fetch mails from pop server more frequently than current Gmail setting. I stumbled up on this script which does exactly the same, it refreshes Gmail POP accounts at every 8 minutes.
The script is available for Firefox (as Greasemonkey add-on), Chrome, Opera, Safari and IE. The script works with a default setting of refreshing at every 8 mins, but If you want to change this frequency you have to unlock the settings by donating minimum of $1. If the script is really useful for you the amount is nothing actually speaking.
For Chrome you just have to download the script, Install it and restart Gmail. You will see the POP3 link with a timer on the right top corner of the browser. You can manage this later from the Google Chrome Extensions page.
For Firefox, If you already have Greasemonkey installed you can go to the developer site and click the download link and install the script. You can manage this script from Firefox Addons > User scripts.