Fix Google Contacts Phone Numbers
Not only since I bought the Nexus S, I'm storing all my contact data in Google Contacts. I also synced my iPhone with it. Over the years a lot of data has accumulated there and one thing that always bugged me was how the phone numbers where all formatted differently. Some had a country prefix, others didn't. There where numbers using dashes, dots or spaces to separate the area code…
Not only does it look like a mess, it may also hinder caller identification or calling might not even work.
So my weekend project was to find a way to reformat all those numbers to a sane format. Of course that's too much work to do manually. Instead I wrote a script using Google's JavaScript API.
The result is the Google Contacts Phone Number fixer.
It will add country codes, remove special chars and even knows about area prefixes of a few European countries.
You can try it without risk, it will only apply the changes once you say so.
It's currently heavily tailored to what I like the phone numbers to look like. And it was only really tested in Chrome. I guess it will work in Firefox but have my doubt on other Browsers 
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If like it, you're welcome - if you don't, just send patches.
Update: The tool is currently broken and can't be fixed until Google offers a working JavaScript API for Contacts again (See Issue Tracker).