For the time being, I am offering licenses for my Minecraft wrapper free of charge. It works on a per-license basis because, for obvious reasons, I cannot allow players to simply connect to any server. Thus, I have to maintain a list of servers and their preferences.
The client fixes a bunch of bugs, provides flight, and quite a bit more. The documentation is at http://mc.earth2me.com/, though I just changed a few of the buttons around (no more engineer mode, G is spawn, X is noclip, R is /thru). I also have yet to write documentation on how to write macros, but once someone shows interest, I will publicize the details on that.
The client also fixes several bugs, such as those historically used by trolls to crash nearby players. It does not, however, patch the major exploit in the server connection process, which can be used to launch a DoS attack. I am currently working on this exploit, and will provide a server patch as soon as I have a solid solution. Note that fixing this bug will prevent clients from connecting without the wrapper, as doing so will change an integral part of the protocol.
Please note that developing this client is a full-time job. I am not interested in stealing your passwords or pulling other nasty pranks. I intent to eventually make a living off products like this.
For more details, feel free to PM me, visit my server, or reply to this thread. To try the latest version of the client, visit http://earth2me.com/minecraft/.