Check out this app: Appa Mundi Tasks

I have seen a lot of rant and request for a Task application into Windows phone. So I decided to look for one on MarketPlace and there are quite a few out there. Among them Appa Mundi Tasks, developed by Appa Mundi Ltd. It is not free - the app costs $3.99 - and a seven days trial is available for download.

Appa Mundi Tasks can be used as a standalone app in case you do not have an Exchange Server 2003 or later. But if you have a need for an online solution so you can create, modify and backup your Tasks, you can always synchronize your list with Hotmail To-Do. That way if you lose your phone, your Tasks list will remain available online. You should already have Hotmail To-Do.

To setup sync between the phone and Hotmail To-Do, open Appa Mundi Tasks on your Windows Phone, tap “...” > Settings > Synchronization Settings. Enter your Windows Live ID or Exchange server credentials. Contact your Exchange server administrator if you do not have this information. For the server name for hotmail, type “m.hotmail.com” and check the “server requires encrypted (SSL) connection”. Validate and start filling your list and synchronize with your Exchange/Hotmail server. Unfortunately, there is no way to auto-synchronize. To view your Tasks in Hotmail, login to your account online and open the Calendar and look under the Hotmail To-Do tab.

Appa Mundi Tasks is a simple to use task app. See list of features below.

Appa Mundi Features:

View your Tasks by due date 
View all Tasks by category
Create new Tasks on your Windows Phone
Edit and Delete existing Tasks
Assign Tasks to categories.
Send status reports via email (Not available in trial)
Synchronize with Microsoft Exchange Server 2003 or later or Hotmail To-Do
Live tile shows number of active Tasks (Not available in trial)
In application reminders (Not available in trial)
Supports recurring Tasks
Keyword search

Download a trial or full version here.