Rename-It! can rename in seconds multiple files using RegExp, that can be in different folders. It is incorporated in the Windows Shell (via Explorer's context menu).
Ranked in these QuestionsQuestion Ranking
Pro Really fast and safe renaming
It can rename thousands of files in seconds and does it in a single transaction so that if anything fails it renames nothing at all.
Pro Can rename the full path
You can change file's directory or rename the full path to the file.
Pro Open source
Pro Can create numbered series
You can ask it to rename so it's Image001, Image002, etc.
Pro Supports regular expressions
Additional to wildcards, and string replacements, it can use RegExp.
Pro Incorporates in the Explorer context menu
Pro Detects cycles and handles them
If you rename A -> B and B -> A (or any cycle), it'll automatically do A -> T, B -> A, T->A.
Pro Command-line arguments
You can create a script invoking Rename-It! from the CLI with some arguments so it performs the renaming and returns the correct exit code.
Pro Can use audio file ID3 tag info
Quite dated - last release or code update at least two years old.