Discourse markers are words and expressions used to show how discourse is constructed. There are a large number of discourse markers. Here are a few of the most common among them.

With reference to

With reference to is a formal discourse marker used mainly at the beginning of business letters.
With reference to your order placed on 12th March, we are pleased to inform you that …

Regarding
Regarding can come at the beginning of a piece of discourse.

Regarding this particular offer – I really don’t think …

As far as … is concerned

As far as … is concerned marks a change of subject by the speaker.

There are no problems about marketing. As far as manufacturing is concerned, I think the best thing is  …

Note that it is wrong to leave out is concerned after as far as …

On the other hand

On the other hand is used to balance two ideas or facts that contrast, but do not contradict each other.

Arranged marriages are unknown in the West. In many Asian countries, on the other hand, they are very common.

Whereas

John is very hardworking whereas his brother lazy.

However and nevertheless

However and nevertheless show contrast. Note that nevertheless is very formal.

She found him physically unattractive. Nevertheless, she agreed to marry him.

The watch is expensive, however, it is worth it.

In the same way and similarly

He was a great player who used his reflexes to stop suddenly while running with the ball. In the same way he used his reflexes to move away from his opponents.

The camel has adapted itself to desert regions by growing a hump on its back. Similarly, the giraffe has a grown a long neck, which enables it to eat leaves from tall trees.

On the contrary

On the contrary is used to contradict a suggestion made by another speaker.

‘Interesting film?’ ‘On the contrary, it was a total waste of time.’