I know I've mentioned this before on here, but the one that really touched him was this: I took a few days to write out what or why I love him/am thankful for him. This could be any and everything including personality traits, sacrifices he's made, a cute butt, whatever. I wrote my list out on paper to make sure there weren't any duplicates, then cut some construction paper into little slips and wrote one "reason" on each slip of paper. I bought a couple bags of balloons and slipped the reason in the balloon. On a light day when he wasn't overly tired and the weather was good, I just went to his work and blew up all the balloons and stuffed his car with them (LOTS fit in an SUV!). I stopped in and gave him a card telling him that I was thankful for all he does for us, and enclosed a large knitting needle and said "use this to find more reasons why I love you". When he went to his car there were all these balloons to pop with the needle, and as each balloon popped, the reason jumped at him. He thought it was funny/silly at first, but it really touched him. He popped enough to drive home safely, then came in with tears in his eyes and brought me to the car to hand him the balloons as he popped them. He's kept them for a couple years, and I finally went and bought a little treasure box to put on his dresser with the "reasons" in it. He doesn't have to read them: just looking at the box brings back the feelings.
Sometimes just throwing an impromptu party is good too. Your son would have fun helping you make a big banner (the banner paper comes in rolls at Office Depot) that says something like "Surprise" or "Happy Saturday" or "We love you" or whatever. Use leftover hats and noise makers and have a silly family day where you celebrate him, do some of his favorite things that you wouldn't normally do (watch a DVD of 3 Stooges or some thing he loves from his childhood, or go to a game, whatever)and then when your son goes to bed you can have quiet time. Things like that go a long way. But what sustains men (and us) in between the "big stuff" is just knowing that we have someone there to vent to, to listen to us, and to be our friend, ya know?