SkyrimForge

Bethesda has finally released the Creation Kit for Skyrim! Also a high resolution texture pack has been released, which can be downloaded from Steam, you can find it on the game's DLC page.

The Creation Kit can be downloaded from Steam (View>Tools>Creation Kit).
For more information and tutorials you can find the official wiki here

Modders rejoice! We’re pleased to announce that the Skyrim Creation Kit is now available!

With the Creation Kit’s release, fans can now upload, download, and install custom content through the Skyrim Workshop on Steam. Get a crash course by reading level designer Joel Burgess’ blog post, and be sure to read up on our list of best practices for modding. Need more help? Don’t forget to to check out the official Wiki at www.CreationKit.com. In the coming days and weeks, we’ll be sharing tutorial videos for beginners and experts alike. Check out the first tutorial above, and visit the Bethesda Game Studios YouTube Channel for more.

In addition to releasing the Creation Kit and Skyrim Workshop, today we’re allowing players to experience Skyrim as you’ve never seen it before with the Skyrim High-Resolution Texture Pack. Before downloading it from Steam, make sure your system requirements exceed Skyrim’s recommended specs before attempting to install, including Windows Vista/7, a minimum of 4GB of system RAM, and a DirectX 9.0c compatible NVIDIA or AMD ATI video card with at least 1 GB of RAM and the latest drivers.

Original article on Bethesda's official blog

Have fun modding!