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The respective Wikipedia article lists most of these already:

• Ext2 Installable File System For Windows: for Windows NT4.0/2000/XP/2003/Vista/2008, read+write access to Ext2/3/4 (the latter two only without journal!), drive mapping supported
• DiskInternal's Linux Reader: for Windows 95, 98, ME, NT, 2000, XP, 2003 Server, Vista, read-only, no drive mapping (a filebrowser UI is available)
• Ext2Fsd: for Windows 2k, XP, Vista and Win7, read+write for Ext2/3/4, journals supported, drive mapping supported
• Explore2fs: for various Windows versions, read-only access to Ext2/3 (probably Ext4 wo journal), no drive mapping (filebrowser UI)
• Paragon ExtBrowser: for Windows XP and Vista, read+write to Ext2/3 (probably 4 wo journal), no drive mapping (access through a special folder in Windows Explorer via Windows Name Space Shell Extension)
• Ext2Read: for various Windows versions, read-only access to Ext2/3 (probably Ext4 wo journal), no drive mapping (filebrowser UI)

Notes ...

The "Ext2 Installable File System For Windows" did not work for me with a 1TB Ext3 filesystem. It told me that the FS was created with an inode size of 256 and Ext2 IFS only supports a max inode size of 128. The FS was created using a SysRescueCD and default options (ie. mkfs.ext3 /dev/sdb1).

My second try was Ext2Fsd and it worked as advertised. I used it only in read-only mode so no clue whether writing is safe (in the release notes of the current version -0.51- there's a bugfix mentioned related to data corruption in case of multithreaded writes using an XP).

P.S.: obviously the above is a very quick summary based on my personal (very quick) review of the homepages of the apps and is reflecting their main features at this very moment. If you find something is incorrect, please let me know.