File Peek gives you a quick and easy look into your files. Use the built-in hex editor; get MD5, SHA1, and SHA256 hashes, and Base64 with one click; or even change the modification and creation dates. The built-in hex editor supports find/replace for easy modification, or for finding strings inside a file. Use the one-click copy for getting a file hash or Base64 encoding for whatever use you need.
Note: Now requires OS X 10.10 or later