Do you often have to engage in debates in class or at work?
Or perhaps you are getting ready for your IELTS or CAE exams?
If so, have a look at these sentence openers.

As a matter of fact...
In regard to...
It comes as no surprise that...
Small wonder that...
It is important to note that ...
On the one hand, ...On the other hand, ...
Luckily, ...
So, to sum it up, ... 
Honestly, ...
Personally, I believe ...
As I see it, ...
For all I know, ...
To my way of thinking, ...
We can safely assume that...
To the best of our knowledge, ...

They are short phrases which may help you gain time when looking for something to say.