I'm a car-free, full-time bike commuter and I want to build a new bike to handle my needs. I am having a hard to finding a frame to build my bike around and thought I would poll the internet for possible suggestions.

Criteria for frame:
Steel frame
Cantilever posts
Ability to fit at least 35mm tires, preferably larger
Intermediate between road and relaxed geometry
A longer than average head tube if possible
Braze ons for fenders
Under 700 dollars for the frame

Frames I have considered: Soma Double Cross, Surly Cross Check, Salsa Casseroll, All City Space Horse. I like the geometry of the Double Cross the best, but I am looking for other possibilities. I want a frame that feels nimble for short rides but is also comfortable enough for riding 40-50 miles at a time.

Any suggestions?

In the 650b tire size, you have Rawland rSogn, and the Velo Orange Polyvalent. The Rawland will be pushing your spending limit. (I'm biased, I have an older Rawland cSogn and a Polyvalent mkI)

I should have specified, I do want to build it with 700c wheels. The Rawland does look pretty awesome though.

Interestingly enough; all the frames you listed were on my considerations list before I purchased a Cross Check.
However; the Cross Check is not my most serious car-free-commuter.
For that I have the Surly Troll

Cross Check:
commute to work, hit singletrack trails on way home/weekend, buy a sandwich and maybe a dvd

Troll:
commute to work, bring full load of groceries home, carried the Cross Check(dissasembled but complete) home from LBS on its back

heh, clear enough?
Both great frames, depending on what you want to do with them.

btw, the Soma Double Cross is a Cross Check clone, similar notes probably apply

IF you Insist on 700c wheels, the Surly Ogre is the 700c Troll analogue; but I can't endore it as definitively having not owned one (too much overlap with already awesome Troll, no need to try one for me; same reasons why I'm not going to get a LongHaulTrucker)

I had the Soma Doublecross as a SS commuter for 3 years until I did a header & bent the frame. I replaced it with the Soma Saga. Longer chain stays, taller head tube. I had to slam the stem to get to my position! Get the 2012 Green, It moves to a seat collar with less slipping problems. The collar is NOT included with the Frame.

https://www.pakebikes.com/product/F8EF09/C%27Mute+Frame

https://store.somafab.com/pacfrfoset.html

$259.99

I don't know about "nimble" , but the price is right....

Since you've considered the Cross Check, did you also look at the Long Haul Trucker? It seems to fit all your criteria, and has a longer head tube than the CC.

If you're close to six feet or more, I'd say go with the Surly Ogre. If much below that, I'd go with the Surly Troll. You can't go wrong either way with the Surly Long Haul Trucker.

Alternatively, SOMAFAB makes some beautiful frames, too!

I your case, I'd pick either the Saga or the San Marcos...

Locate a mid-1980s Trek 620 or 720 frame. Meets all of your needs and will be finely made, too. My $0.02

The Ogre is pretty awesome. However, I already own a Karate Monkey and do own a set of big apples for riding on pavement. So the Ogre/Troll would be a little redundant.

Now that I've been contemplating, I might just follow the flock and get a cross check frame. I wish Surly's complete Cross Check wasn't a weird set of components otherwise I might consider just saving time and getting a complete. But alas, I'm still just unsure about the geometry. I'm 6'1.5" with a 34.5" barefoot inseam (floor to crotch). The 58cm cross check seems like my best bet as I don't want a super long top tube, but from lurking around the forums I've noticed people having a hard time getting the right size on the cross check. I know bike fit is not possible over the internet, so I don't even know why I'm mentioning it. I guess just to see if anyone has had experience with having their cross check actually fit them like a glove--as that is what I am after.

Have you considered the Handsome Devil? It's got most of the features of the Cross Check but with a lower bottom bracket and taller head tube. Unfortunately, it only comes in a few sizes.

The Civia Kingfield looks nice too

The Motobecane Fantom CXX is the same frame as the CC, with a nice spec of Sram Apex for $800. I have one, the tiny 42cm size, and I like it a lot.
https://www.bikesdirect.com/products/...fantom_cxx.htm

Double Cross, mine has 15,000 miles on it and it always puts a smile on my face. It will take 700x38 Schwalbe Marathon tires and fenders.

Winter mode;



Summer mode;

Not even close;

Soma: heat treated Tange Prestige
CC: 4130

Soma: Vertical Drop-outs
CC: Horizontal drop-outs

Soma: Semi-compact geometry with a sloping top-tube
CC: Horizontal top-tube geometry

They both can be great bikes, but the differences are substantial.

That looks pretty awesome. That's the Double Cross DC right? Looks about my size too, is that the 58cm or 60cm? Do you happen to have any experience with any of the other mentioned bikes just for comparison sake? When I was heavily considering the Double Cross I originally thought I'd need the 60cm being 6'1.5" bare foot and over 6'2" with shoes on. But then I realized it has a super long top tube. Mind you, I want to be able to go fast, but not feel like I'm racing to the grocery store as it would be my full time commuter/short touring bike. I've tried to figure out why the Cross Check gets so many more votes than the Double Cross in general despite the Double Cross having better steel. I've never ridden either one unfortunately. Any input?

It's a 60cm size DC model. A 58cm size would have also fit me, I'm 6'0", but long limbed and I like a stretched-out fit.

The Surly is better if you want the single speed option or if you want 700x40 tires. The Soma can be a little more sporty, mine makes an ideal century bike. Since you have a Karate Monkey for heavy-duty use, you might enjoy the Soma more than the Cross Check.