First, take a look at the Bukkit wiki guide on uploading texture packs, to make sure your pack meets specifications. If it does, continue on!
How to Upload your Packs to Bukkit
Step 1: Go to dev.bukkit.org and click "Create a New Project".
If you are not logged in, you will be taken to a log in prompt. Log in with your normal Curse credentials to get started!
Step 2: Choose your Category and enter your project information.
Be sure to click Client Mod, as seen below:
This will take you to the project creation page. Please only upload files you have made yourself. Fill out all information as detailed as you can regarding your texture pack! The more accurately you fill out the information, the more likely you are to have your pack approved with no problems!
Under Primary Category, choose Texture Packs.
Be sure to summarize your project and leave a detailed description! This is important for players to know what your texture pack is. The summary is especially important as it is what will show up in the Curse Client.
Please remember that all projects and files are hand-approved in an approval queue, and will not be instantly available. Curse does this to help ensure all users' safety when downloading files.
Step 3:Upload your File
While you are waiting for project approval, you can still upload your file! On your project's page under "Project Management", click Upload File.
This will take you to the following page, where you can give your file a specific name, select the game version, file type, and enter in a change log.
Remember that all projects and files are hand-approved in an approval queue, so your file will not be available instantly.
After that, you're done! Your file will be in the Curse Client as well as on Curse.com, which you can link to and advertise to your heart's content! Also, be sure to keep an ear to the ground about uploading texture packs, maps, and more - there are goodies on the horizon we can't tell you about just yet, but soon!
Don't forget that the Curse Client also has world backup and restoring features, loads of texture packs, and more. Give it a try, and tell us what you think!