How are you getting the requests, via email or messaging?
There are several applications that allow you to create Tasks or Calendar events from messages and SMS.
PocketDay and Empower email viewer are two that come to mind. Another really good one is Add To Calendar (BerryLogic - Developer of Add To Calendar for the BlackBerry
for that one, the other two are easy to find with a Google/Yahoo search).
If you're getting the requests another way, and then creating the reminders, either tasks or a calendar entry will do the trick. If you're working with lots of them and they have to be juggled, you might want to look at ToDo and IdeaMatrix as already suggested. As I recall, you also can login via the web to the latter and sync with your Berry and vice versa.