Source Sans Pro in action on 12ish.com

Under the hood

.header-1 { font-family: 'Source Sans Pro', Helvetica, arial, sans-serif; font-size: 36px; font-style: normal; font-weight: 300; letter-spacing: -1px; line-height: 39px; text-transform: none; color: #FFFFFF; }
.header-2 { font-family: 'Source Sans Pro', Helvetica, arial, sans-serif; font-size: 35px; font-style: normal; font-weight: 100; letter-spacing: 0px; line-height: 38px; text-transform: none; color: #FFFFFF; }
.content-1 { font-family: 'Source Sans Pro', Helvetica, arial, sans-serif; font-size: 27px; font-style: normal; font-weight: 100; letter-spacing: normal; line-height: 35px; text-transform: none; color: #FFFFFF; }
.content-2 { font-family: 'Source Sans Pro', Helvetica, arial, sans-serif; font-size: 16px; font-style: normal; font-weight: 100; letter-spacing: normal; line-height: 22px; text-transform: none; color: #BEBEBE; }