Google Sync for iPhone
Today Google offically released Google Sync for mobile phones including …
Synchronize the built-in calendar and contacts on your iPhone with your Google account.
- Get Google Calendar events on your device
- View multiple Calendars in different colors
- Synchronize your Contacts with Google
- Have changes pushed directly to your phone
While i have been using NuevaSync and have found it a great option it still lacks a little polish and can be a little flaky.
So I have today switched to Google’s offering. It was simple to setup by following the instructions here
I did have some issues with it not syncing all my calendars or the colours associated with it.
After some digging around I discovered this about setting up the calendars you want to sync…
Sync: Choose Which Calendars to Sync
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Google Sync allows you to choose up to five calendars to synchronize with the Calendar app on your iPhone.
To select which calendars to sync to your iPhone, follow the steps below:
1. Open the Safari browser on your phone and go to http://m.google.com/sync.
2. Sign in with your account and select your phone from the list of devices you’ve set up for Google Sync.
3. Bookmark this page so you can return to it easily.
This got it all going in a flash as well as colours 
http://www.google.com/support/mobile/bin/topic.py?topic=13587