It depends on what your target audience is and how interactive the site you are building is.

jQTouch:

heavy on the CSS, light on the JavaScript, MIT license

For a framework that provides a quick start, but not a lot of documentation unfortunately, use jQTouch. It requires very little to get started and coding is fairly straight forward. It uses CSS classes for detecting the appropriate animations and interactions.

Sencha Touch:

almost completely JavaScript, GPL not for use on commercial sites without a license

If you are building a complex enterprise application with a lot of visual interactions, I would strongly recommend Sencha Touch, it is heavily documented, with a strong professional team providing support.

M-Project:

MIT license, heavy on the JavaScript, appears to be in Alpha, may be buggy

Although I have never worked with M-Project myself (thanks for pointing it out) it does appear to be a very robust, and the coding style appears to be very similar to Sencha Touch, which is based on ExtJS, so if your team already has experience with ExtJS, it might be wise to consider one of these frameworks.

Nimblekit:

This appears to be for iOS only, not a good thing if you ever decide to expand your application to Android or some other platform.

Wink Toolkit:

appears to be MIT, or some variation there of
In my opinion, wink seems to have plenty going for it, but the documentation feels cold

jQuery Mobile:

Dual license MIT or GPL 2, just the right mixture of JavaScript and CSS

I will let someone with more experience talk about the merits, but jQuery mobile (though it is in alpha as well) is backed by a strong team and a community of supporters by extension of the core jQuery library. Probably the best choice for anything except the most enterprise centric applications.

Titanium:

Titanium is not an HTML5 mobile framework, it is a javascript based interface to native code modules included in the framework. It is a fairly straight forward framework, but I would consider the documentation sparse.

Bottom Line:

1. jQuery mobile - as long as your app is not enterprise centric

2. Sencha Touch - if your application is enterprise centric or heavy on user interactions

3. jQTouch - if what you are looking for is a simple framework to get started with quickly, but you don't need a lot of gusto.

4. Titanium - if you are more concerned with having actual native controls in your application

Demonstration Apps

There is an open source project, PropertyCross, which demonstrates the same application implemented with a range of cross platform frameworks. It is very useful for comparing the code, development experience and end-user experience of the various frameworks.