What is the best way to say I LOVE YOU?

No need to say I love you because you are with her for last 3 yrs . Be with her and wait when she feels your love and affection towards her.

Go man and just say "I LOVE YOU". You are with her for yr and I think she must be knowing that u love her alot. I f still u want to express u can give her bunch of beautiful roses, hug her and kiss her and wisper the magical words to her ears.

pick up the mobile send her a sweet sms and wait for her response

In whatever way u say it.....it should be from ur heart. if u say "I love u"....u should mean it. and don't repeat them plzzz else these lovely words will loose their charm..... Go ahead and say it !!! what r u waiting for???

Best way is ur behaviour. It'll never fail. I'll be specific in a new discussion.

Surprise her! Love and Humor are the foundations of a relationship, so be shure you keep her smiling while she's around you. Right a song with her name in it, invite a few friends that play guitar, and do some sort of serenate. Put in her somthing to cover her eyes, and take her to a beautifull place with a picnic waiting. Show her somewhere, like the top of a building, the roof of your house, a rock on the top of the moutain near you, at night, to see the stars... say beautiful things, make her feel a princess, make sweet gentle love to her (add some candles to the room also)... Worked for me :P

how about making her feel she is special? and letting her discovewr new things about you everyday? this should keep the spark in your relationship sparkling.. just tell it with your heart in it.. whisper it in her ears.. say it in action.. it depends on your style.. i agree with rossoz, and the best response mark you gave is something he deserve..