Capitalize
From Shopify Wiki
capitalize(input)
This filter returns a capitalized form of the input string.
*note: capitalize only capitalizes the first word in the returned string.
Example:
<span>{{ variant.title | capitalize }}</span>
A variant.title of "blue shirt" returns "Blue shirt". If you need this to return "Blue Shirt" you will need to use the text-transform CSS property.
Information at w3schools.com: http://www.w3schools.com/Css/pr_text_text-transform.asp