You can also be really really formal saying 사랑합니다/sa-rang-ham-ni-da

It's all here: http://www.youtube.com/watch?v=sg3HH1vt6Q8

oh.. ok kamsahamnida

사랑해 (saranghae) and 사랑해요 (saranghaeyo) both mean "I love you" Only 사랑해요 (saranghaeyo) is more formal. In korean you have to adress formally to.people older than you, here the ending 요 (yo) makes it more polite. So if you want to say "i love you" to someone older than you, you should say 사랑해요 (saranghaeyo) anto someone of your age or younger 사랑해 (saranghae) Cheers ! 화이팅!