What tool can do a visual comparison of two sections within the same file?

I use Beyond Compare (not free, but I think a shareware version is available). You can select the same file for left and right sides, then right-click the beginning of your section on each side and select "Align Manually". This would allow you to compare two sections of the same file relatively easily.

Overall, I highly recommend the product. I haven't tried version 3, which is what they currently have on their Web site, but version 2 is a fabulous tool. A+

Emacs Ediff.

I use UltraEdit for most of my text editing and they have a product called UltraCompare that does a visual compare.

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Update by Mofi

UltraCompare Professional supports also a comparison of text snippets in addition to entire files.

After starting UltraCompare, select Text Compare in menu Mode if not already selected. Select in text editor the first text block which should be compared, press Ctrl+C, switch back to UC and paste with Ctrl+V the block into left text area pane. Switch again to text editor, select the other block in same file, press Ctrl+C, switch back to UC, click into right pane and paste the block with Ctrl+V. The two blocks are immediately compared and the differences are displayed.

Such a text snippet comparison for two blocks in same file can be started also directly from within UltraEdit. Select the first block in file, press Ctrl+C, Ctrl+N, Ctrl+V and Ctrl+A to copy, paste and reselect this block in a new file. Select the second block in file. Execute command Compare from menu File in UltraEdit with option Compare selected text automatically being enabled and click on button Compare. UC Professional is started with just the 2 selected blocks for comparison.