Got to disagree with you on this one Giok,
Songs like "An Ubhal as Airde", An Ataireachd Ard", "An Sabhal Aig Neill" and "Tillidh mi" are part of the current gaelic reportoire and have lovely hebredean melodies, not to mention great words.
As for non gaelic songs try "The Summer Walkers" from "The Stamping Ground"
Sometimes when you journey
Through the pages of a book
You're taken places beyond words
You let them speak the truth
Today I've opened treasures
That my eyes could scarce believe
They're the words of confirmation
Everything that makes me sing

Summer comes to Sutherland
And you bend the hazel bow
You harness up the ponies
And you head out on the road
By Kilbreck and Altnaharra
You journey to your rest
With the guiding might of Suliven
For the campsites of the West

And it's up by the Shin
And up by the 'Naver
And the long winding shores
Of Loch Maree
By Ben Hope and Ben Loyal
By Stack and by Arkle
The road reaches far
Now the summer is here

Now your words are not of sentiment
Shallow or untrue
But wels of living water
And from their clear deep sides we drew
The songs, the tin, the horses
This country's great and ancient wilds
Your faith in God and man and nature
And the keeness of your guile

(Chorus)

So have you stood out on Coldbackie
At the time the sun goes down
Or up on the king of campsites
In he hills about Brae Tongue
That's when music filled your evenings
It's all so different now, this world
For you were the summer walkers
And the fishers of the pearl.

(Chorus)

So as we close another chapter
That we label Archive Gold
Still the Conon flows each morning
And the dew falls from the sloe
But today you took me walking
Through a land that we have lost
While our children sit at websites
With no access to the cost

(Chorus)

This song has a great tune and if you go into a pub in Ullapool and sing it, the chances are that people will join in with you on the chorus.
Well if that's not folksong then I've been listening to the wrong stuff.

Cheers

Andy