Not a national anthem but I saw a couple of people mention Australia. Here are two of my favourite Australia clips...

http://uk.youtube.com/watch?v=pq1wg76bDpo
http://uk.youtube.com/watch?v=wJ70wtD-fLA

Canada's unofficial national anthem is much better >=)

In days of yore, from Britain's shore,
Wolfe, the dauntless hero came,

And planted firm Britannia's flag,
On Canada's fair domain.
Here may it wave, our boast, our pride,
And joined in love together,
The thistle, shamrock, rose entwine
The Maple Leaf forever!

Chorus:
The Maple Leaf, our emblem dear,
The Maple Leaf forever!
God save our King, and Heaven bless,
The Maple Leaf forever!

At Queenston Heights and Lundy's Lane,
Our brave fathers, side by side,
For freedom, homes, and loved ones dear,
Firmly stood and nobly died;
And those dear rights which they maintained,
We swear to yield them never!
Our watchword evermore shall be,
The Maple Leaf forever!

Chorus:
Our fair Dominion now extends
From Cape Race to Nootka Sound;
May peace forever be our lot,
And plenteous store abound:
And may those ties of love be ours
Which discord cannot sever,
And flourish green o'er freedom's home
The Maple Leaf forever!
Chorus:
On merry England's far famed land
May kind heaven sweetly smile,
God bless old Scotland evermore
and Ireland's Em'rald Isle!
And swell the song both loud and long
Till rocks and forest quiver!
God save our King and Heaven bless
The Maple Leaf forever!
Chorus:

You can hear the tune here:

http://www.youtube.com/watch?v=m_SfHckklr0

Though it sounds better on bagpipes imo.

The worst anthem I've ever heard is the American one. It makes me cringe. Granted, other anthems might make me cringe, but I don't understand the language, so I have no clue what nonsense they're spouting.

Belgium has some sort of officious anthem too: http://www.youtube.com/watch?v=2M9LnTfeI80