Despite not officially being available for the original iPad, the new iPhoto iOS app and iMovie can be manually copied to the original iPad.
Apple Insider details the steps you need to take to install the apps on the original iPad, which is presumably not officially supported by the apps due to the lack of a camera.
You'll need Apple's free iPhone Configuration Utility, which is available for Mac or Windows. Once this is installed, connect your iPad via USB to your system and select the apps you want to manually install by adding them to the library.
Once you've bought the apps in iTunes, you can find them in your Music folder under iTunes/iTunes Media/Mobile Applications.
In the Configuration Utility library, click on the Install button for each app under the Applications tab. The utility copies the app and by all accounts it will work normally on your first-generation iPad.
We haven't yet tried this out for ourselves, so cannot verify that it works, though we've heard of several people who have performed the workaround successfully. Apple Insider notes, though, that in some cased iTunes may show warnings that it is no longer authorised for apps on your iPad.
Should this happen, click Authorise and it will dismiss the alert. If you click Don't Authorise, it will remove the apps you installed manually.
If you've managed to perform this manual install successfully let us know in the Comments section below.