1) Compliment him: guys need a bit of reassurance too..don't just reap in the compliments and smile...tell him how handsome, funny or sweet he is..etc..
2) It's the little things that count: often guys need to feel that they are needed and appreciated by their girlfriend. Whether it's just a simple "you mean so much to me" or even calling them up unexpectedly to tell them you love them. I learned the hard way when my 'boyfriend' said that he just wanted me to call him up sometimes without having a reason to.
3) Indulge him: massages, little gifts, cooking him a special meal, taking him somewhere romantic, helping him out when he's busy etx. It doesn't have to be Valentine's day or his birthday even..just surprise him.
4) Cook for him (taken from point 3): i think this one's worth repeating cos i've never met a guy who doesn't enjoy good food. I've cooked for my boyfriend: from chocolate cake, muffins, and cookies..to pastas, casseroles and roasts. There's a billion other recipes you could try..and you don't have to be a pro.
5) Intimacy: yeah couldn't have a top 5 list without mentioning it. it doesn't have to be sex (im sure he'd like it though)..it could be anything from learning a new way to kiss..treating him with a soothing massage, having a bubble bath together, or if anyone's every tried it..showering together even. it would be good for you too..but make sure you make time where it's just all for him.