Arial with Curious Sans in action on bbc.co.uk

Under the hood

.header-1 { font-family: Arial, Helvetica, freesans, sans-serif; font-size: 16px; font-style: normal; font-weight: bold; letter-spacing: normal; line-height: 22px; text-transform: none; color: #FFFFFF; background-color: #369741; }
.header-2 { font-family: CuriousSans-Bold, Arial, Helvetica, freesans, sans-serif; font-size: 34px; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: 34px; text-transform: none; color: #333333; }
.content-1 { font-family: Arial, Helvetica, freesans, sans-serif; font-size: 16px; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: 22px; text-transform: none; color: #333333; }

Arial is available from Fonts.com and MyFonts.