Just wrote this tool, to allow instant transformation of data into following formats:
base64 encode decode, urlencode decode, md5 and sha1 hashing, rot13, addslashes and htmlentities.
Really cool to select all, then compare these encodings side by side.
This tool can be used to decode URLs, encode base64 for tricky characters or decode for checking mail (mime) content. Also for performing md5s, sha1 hashing, etc.