Resizing under TouchWiz requires that the widget be written to support it. Here's the ones I have found. In cases where there are multiple widgets by the same name, it will be the Samsung version.
AccuWeather.com
Agenda
Ap Mobile
Bookmark
Email
Picture Frame
For those that don't know how to size them:
1. Touch and hold in the lower left corner of the widget like you were going to move it.
2. When it changes to move mode, release the widget. A set of grid lines will appear showing the allowable sizes.
3. Using the thumb icon in the lower right corner of the widget, drag the widget to the desired size.
4. Touch anywhere else to exit size mode.