1. Sex out of nowhere. That's not to say you should jump on top of him from your hiding spot as soon as he gets home and just start going at it (unless he's really into having you sexily pounce on him). But coming home to find you dressed up in lingerie (or, if you don't want to spring for lingerie, just naked) is great.
2. Having a dinner already made for him. Yeah, the first two items on this list are sex and food, because these things run true and deep through a man's veins. Coming home to a fancy steak dinner or even a freshly delivered pizza when he thought he was going to have to cook or pick up food after a long day of work is a huge relief.
3. A last-minute date night. It doesn't have to be anything crazy, but going out to dinner on a Wednesday for a few drinks and some tapas can help get him through the rest of the week. He's not going to say no to that.
4. Tickets to a game or concert. Maybe a coworker had to unload some tickets last minute, so make sure his schedule is clear and surprise him. And if it's for something you totally hate, you can always make it seem like you want him to take a friend.
5. A present for no reason. Everyone loves getting presents on their birthday, but you know they're coming, because we're all presumptive and self-centered. Grabbing him a new shirt just because you thought he'd like it can brighten his day.
6. MORE SEX. Yeah, surprising him with sex never fails. Grabbing him when you're out in public and pulling him into the car or a bathroom is a nice way to surprise him (and possibly any bystanders...make sure wherever you go is private; basically, don't have sex in public, it's illegal).
7. A quick love note tucked into his briefcase. Do people even use briefcases anymore? I guess the better term is laptop bag, but I digress. Getting to work and knowing he's about to start a long day can be depressing, but realizing you left him a little note will cheer him up.
8. Grab a bunch of his favorite snacks. Maybe he likes crunchy Cheetos and you're into puffed. Perhaps your house is split on the Cool Ranch/Nacho Cheese initiative. Or maybe he's one of those weirdos who considers "celery and peanut butter" a true snack. Just get him a bunch of his favorite stuff the next time you're out buying groceries anyway because everyone loves snacking.
9. Make him think you're dragging him along to the craft store, and then go to the movies instead. If you really want to milk this, go back and forth on it several times. But it'll be a relief for him to know that instead of having to stand around looking at a bunch of yarn for an hour, you're going to see a movie he's been dying to see for a while.
10. Sext him when he's in a meeting. Just make sure he's not presenting. You don't want to sext the whole meeting.
11. Take care of that project he's been putting off. Maybe he needs to gas up his car or drop some stuff off at the dry cleaner. Everyone has those chores they need to do but can't be bothered with. If you take care of it for him, he'll be so happy, and it's one less thing for him to never get to.
12. An impromptu anniversary, like the two-year, three-month anniversary of the first time he texted you. Come up with a reason for an anniversary and spoil him any way you can. Maybe it's the just a massage and dinner, or a gift, or just cuddling and a movie, but make him feel like you're celebrating a milestone, even if it's goofy.