If you're fed up having different applications for different systems then GCalSync could be the thing for you. However, an early health warning, this is in early stages and there are some problems.
First, the good news: GCalSync allows a two-way sychronisation between Google Calendar and your phone's built-in calendar meaning you only ever need to add important dates once and then upload them. Also if an event has been changed in Google Calendar since the last sync then it will be updated on the phone.
Now the bad news: If an event has been changed on the phone, the changes will not be uploaded to Google Calendar; reminders are not supported; recurring events are treated as multiple events. However, despite the problems there's great potential here.