More formal:
* Furthermore, it is important to note that...
* Moreover, it is crucial to understand that...
* It is also essential to highlight that...
* It is worth emphasizing that...
* Of paramount importance is the fact that...
Less formal:
* Another key point is that...
* It's also worth mentioning that...
* Don't forget that...
* Importantly, ...
* To be clear,...
More specific:
* Specifically, ...
* In particular, ...
* More importantly, ...
The best rephrasing will depend on the context and the tone you want to convey.