You can get CMS Static Block urls in following ways:

1) To get Base url in CMS block,

Syntax: {{store url=””}}

2) To get Skin url in CMS block,

Syntax: {{skin url=’images/imageName.jpg’}}

3) To get Media url in CMS block,

Syntax: {{media url=’/imageName.jpg’}}

4) To get Store url in CMS block,

Syntax: {{store url=’mycmspage.html’}}