Prowl is the Growl client for the iPhone OS. Notifications from your Mac or Windows computer are sent to your iPhone or iPod touch using push. Prowl has an extensive API, which allows your scripts to integrate beautifully.
Prowl is the best couple dollars I’ve spent on the iPhone in months. I bought it a few weeks ago and it was really easy to set up, and now I get notifications for Transmission, confirmations of Dropbox syncs, Twitter mentions and direct messages, Email pop-ups (instead of sounds, which I don’t want), and all sorts of other little notifications that let me know what’s going on as long as I have my computer on at home. There are ways to make it not send notifications to your phone while you’re at your computer based on idle time or if your screensaver is active. You can configure it to offer to open up different iPhone apps (from a predefined list) based on search strings found in the Growl notification, so you can make it open up your Twitter client or IM client, for example.
The developer even addressed one of Apple’s Push Notifications system’s greatest weaknesses— the lack of “quiet hours”— by letting you specify a time of day during which you want push notifications to be squelched so you don’t have to manually turn off push notifications every night before you go to sleep. I highly recommend this app if you have a Mac and use Growl.