HTC has released an update to its HTC Sync software for the HTC Aria, and along with it comes the ability to install third-party applications and enable mobile network sharing. Hallelujah! While this isn't nearly as handy as installing the applications directly from the phone, it's a huge step in the right direction. The addition of mobile network sharing is a huge boon as well, just remember to keep an eye on your data usage if you've switched to one of AT&T's new plans.
HTC Sync is also a great way to sync calendar events and contacts with Outlook (or Outlook Express/Windows Live Mail) on your Windows PC. Sorry, Mac users, you can sit over here with us Linux guys and grumble. Hit the source link to check out the requirements and download the software -- you'll need your device serial number, click and enlarge the pic to the left for help finding it. [HTC Aria Product Support] Thanks to everyone who sent this in!
Update: As Spary points out in the comments below, there was an apparent SNAFU at HTC and this update does not enable sideloading, nor does it change any settings on the device itself. HTC has reached out to Engadget and apologized for any confusion, and says their website will be updated with the correct information Monday. Felt good for a couple hours though!