On my Surly 1x1 commute/kid-towing/in-town cruiser I have a CK headset, CK SS hubset, Thomson Post and stem, Easton carbon low-risers, XTR brakes, XT pedals, and cheap Campy Veloce triple cranks, and a Fizik Airone saddle. LOVE my bike. Its so much fun to ride.

Don't skimp on the brakes. You hit them all the time and if they feel like crap on day-1, which Tektro's do, you will hate them more and more every day you own the bike. You can get a nice set of DA 7800 brakes for ~100 used and will have some of the best and lighest stoppers out there. I like Campy brakes and have Skeleton's on my road SS. Pretty and light.

I don't like Sugino cranks, except some of the nicer road-style cranks. Omniums like others have posted. I have both of my SS's setup with campy rings, and I wanted the look of older Campy for my MTB, hence the Veloce. IMHO, good road cranks are far superior than so-called single speed / fixed cranks. If you pick up an old aluminm Chorus/Veloce/Centaur the fit and finish is light years beyond the the Messengers and they are dirt cheap. They just happen to use a funny bolt pattern (135 bcd)

Get a Brooks if you must, but I have 4 bikes, 3 have Fizik Airone, the other is a FS MTB which I don't want to muck up a nice saddle on the trail. Brooks saddles are too much for looks IMHO. My Fizik weighs 115 grams and is comfy as all get-out. Hate to see what a Brooks would weigh, and would never want to sit on one.

Also, Freewheel. White Industies Eno or CK SS Hub (If you can get them to make you one in 120mm spacing, I have only ever seen them in 135 spacing). There is not better options out there and both are flawless in execution.