Since I don't always have RTM open in the browser I usually add tasks by sending emails to my rtm account.

Therfore I created an outlook mail template and stored it to the desktop.
(By that you can re-use the same template thousands of times again and again)
The template contains the following:
receipient = rtm-mail-adress
subject = RememberTheMilk
And the body of that mail looks like that:

Task:
Priority:
Due:
Repeat:
Estimate:
Tags:
URL:
Location:
List:
-end-
The following entries are valid:
Location: home / office / any other adress
Tags: @nextAction / @reference / @delegated / garden / phone call / any other tag
List: Inbox / All tasks/ Work/ Private / Studies / Sent / any other list


This way it takes only some seconds to fill out the template and send this mail (while the template itself remains on the desktop)