I was looking for same, and as I run 11.04 I can't use something like google-task-indicator even if I wanted.
As Evolution is nicely integrated with date/time indicator, I thought to take advantage of that.
I first tried RTM which I thought to interface with Tasque but found that RTM integration in Tasque is buggy. Then I left RTM interface for later and tried to export RTM events to my Google calendar account which I integrate in Evolution. Either importing RTM event ical calendar in Google calendar or directly in Evolution as new calendar, resulted in calendar without events, although I created couple of test tasks in RTM Inbox and give 1 hour time-out for both scenarios.
Here, another possibility which does not seem too useful to me, would be RSS export from RTM and then use some RSS indicator to track this tasks, but already discouraged by previous writing I looked for other approach.
So, I made new calendar in Google calendar, called Tasks, and added it to my Evolution calendars. This may not be solution for all, but for me it's enough. I can add "tasks" thought Evolution "Add event..." action from date/time indicator, but for quicker way I made "shortcut" script called "add-task" wrapped around googlecl and put it in
google calendar add --cal Tasks "$@"
and then from terminal I can quickly add task like:
$ add-task "Finish that paper for 3 days"
which will show in date/time indicator (pale yellow colored), for next 3 days:
This is one working possibility, and it seems easy to make yet other different approaches, with or without downloading too much software
Hope someone finds it useful ^_^