He's Almost 18! What Should We Do?

Buy him a ticket to Europe and send him on his way for several months. He'll find out who he is and what he is not. He'll make new friends and have a fantastic adventure.

When my older son turned 18 we plotted with his friends and a few spent the night. I made a big surprise brunch for him. He came downstairs with those friends and a bunch more were here. It was low key but he loved it.
My mom threw me a surprise party when I was 18 too and I never forgot it.
Mu younger son would have hated to have a surprise party so we didn't do that to him. Just a family plus friend dinner and let him celebrate with his friends on his own.

He will be an adult on this birthday ask him what he wants to do. I am glad my parent's did. All I wanted was bowling shoes, a bowling ball & bowling bag. My family bowls for fun & I didn't want to have to rent shoes, look for a ball or have a hard time carring it, plus I didn't want everyone elses germs. Sometimes when you grow up your wants become more simple. I was elated I got all three & those were my only presents. My whole family pitched in (parents, aunts, uncles, grandparents, brothers & sister). I still have them & I still bowl with my family 16 years later. I had a family party without decorations & my two favorite cakes.

We always had low key birthdays growing up. However, on our 18th birthday we were taken out to dinner. On my 18th I had a few friends over to just hang out and my mom made lunch and a cake. It was one of my favorite days.
My girlfriend did a surprise party for her daughters 18th. In advance she asked everyone to provide her with a handwritten memory of her daughter and a photo if they had one. She put this all together in a scrapbook and had it out at the party.

When I turned 18, my mom and dad filled the cab of my truck with balloons... while i was at school. Then when i got home my room was full of them, my bathroom was full of them. (personally i thought it was a little overkill...) but it made for a rememorable night.

I agree, ask what he wants. Though you can also conspire with is closest friends and do something special also. Usually at this age friends have an idea of what he will want to do, or not want.
For my 18th, my mom and friends conspired against me, my friends came in my room at 5 in the morning and kidnapped me (after putting me in the most hidious things they cold find). We went out to breakfast before school and I had a blast. It was definitely memorable. That evening I had a party at the restaurant of my choice with my family.

Well, when I turned 18 I hosted my own "Denial of Adulthood" party (actually a ritual recognition of the passing of childhood, of course, not actual denial) ... I invited half males and half females, my closest friends, and told them to dress age 5-ish, and we were going to do kid things (I had a bunch of saved wrapping paper scraps and glitter and we used kid scissors and glue sticks to decorate those pointy party hats ... some of my most precious pictures are actually of those friends wearing those hats ;) ) ... and then we went to the local park to play on the swings and the rocket slide (although one young man we literally had to pick up, in a friendly way, and carry the first half a block before he acquiecsed(?sp) and walked with us ... he later thanked me for doing it, that it helped him too with the transition, even though at the time is was WAY outside of his comfort zone)

When one of my brothers turned 18, he did the now-I'm-18 neighborhood tour: went to wherever it is boys register for the draft and took care of that, then went to the store and bought 1 pack of cigarettes, 1 issue of a pornographic magazine, and 1 lottery ticket (he didn't as far as I know do anything much with any of those items ... the cigarettes dried out in his room as I recall ...) ... same "coming of age ritual" impulse as I had, I suppose (I didn't like it because of the pornography part, but it was an interesting way to recognize the event ... and since he had to register for the draft, which of course I hadn't had to do, it seemed like doing something anti-social was a balance of sorts in coming-of-age-in-America, sigh ... )

So, I don't necessarily recommend either of those ... but from them I suspect your son has ideas about what would be a significant experience for him at this time. (Myself, I wish more churches offered some sort of effective recognition for adulthood ... that would have meant a lot to me, anyhow)

My eldest daughter turned 18 a couple of years ago, and it was a VERY big deal, as she had quite a turbulent adolescence.

We hosted a "do-it-yourself" sushi potluck party (her favorite food). I made the sushi rice, provided essential ingredients, some fish, and many sushi rollers, sushi plates, soy sauce dishes, chopsticks, and plum wine. We invited a few of her closest friends, and all the adults who have been part of her life growing up who are special to her--including her pre-school teacher. Everyone brought additional ingredients and plum wine and made sushi together.

My gift to her was that I spent DAYS going through every picture I have of her, from birth on, scanning them into our computer if they weren't digital (most were not) and making them into collages. I then used them in a slide show on the computer during the party, and ALSO printed them on really good photo paper and turned them into a keepsake book for her.