While there are options for accessing files on your phone's SD card, Webkey takes it one step further and essentially allows you to control your rooted phone from your computer.
To get started with Webkey, head to the Market for the download. After running the application, select "Start Service" and an IP address should pop up, along with a temporary admin username and password. If your carrier allows for these types of incoming connections, you are all set. Unfortunately, this will not be the case for most users.
If this setup does not work, check the box marked "keep alive connection to androidwebkey.com" and also specify a unique username by clicking Username at server. Now to access your phone, you'll just need to visit androidwebkey.com/username/. If you don't want to deal with these temporary credentials, click Users settings and create a new username with all of the permissions enabled.
Once you are logged into Webkey online, you can do essentially anything. You can start calls, send and receive text messages, and even browse the web. The service relays mouse clicks as touch events, so anything not requiring sensors or voice should be do-able. The service also has a pretty handy file browser, where you can access not only SD card files, but anything on the device. Furthermore, if you feel like tinkering around, Webkey has a fully functioning terminal emulator.
Apart from the somewhat obvious little general uses, this service allows for some interesting things. There is a GPS tab on the interface that allows you to locate the device using both GPS and Network coordinates. This is perfect for finding a lost phone, or one that has fallen into the wrong hands. Also, there is a pretty in-depth call log with a pretty neat visualisation of the data. It graphs calls that last longer than a half minute day-by-day, with a distinction between incoming and outgoing. This could be useful for those of us watching our minutes. Another interesting feature is chat within Android Webkey. Multiple users can be specified for access with varying permissions, all while having communication allowed between these users. This could come in handy if you've got a less than tech-savvy friend (or perhaps if you are that friend). HIt the link to try it out, and let us know what uses you come up with in the comments.
Webkey is a free download for rooted Android phones.