After I decided to start a tumblelog (again), the first thing I did was finding a desktop client. For now, Tumblr does not support XML-RPC protocol, but they do have API.
I’m not familiar with API, so I searched for solution. Luckily, I found Tumbleweed. Login using Tumblr account, and you can start writing. If you have web camera, you can also capture using it, and post it as photo. What I like from Tumblweed:

• The interface is clean, easy to understand.
• Support multiple tumble format — of course!
• It also support tags and timestamp modification
• Support multiple tumblelogs from Tumblr, using Tumblr domain or custom domain.

But, there are some limitations (it’s more about my personal preferences):

• When writing a “Quote”, there is no textarea to write the description. It’s only an “input” type.
• Entry history. If you have many contents, you only see your last 20 entries.
• Inline editing. All posted contents can’t be edited from the interface.

Those features seems not available for now — based on my observation. But, I’m fine with that since this is the best Tumblr desktop client I found so far. If you have any recommendation, please share.
Anyway, if you want to install Tumblweed, you need to have Adobe AIR installed first.