So what other units would I add to this to give me options, and variety for different scenarios and opponents (I'm not a huge fan of list tailoring, but if there's one army that goes to war with a big enough array of equipment to be responsive to their enemy and the battlefield, its space marines.
The one missing item that stares out at me from the original list is that the hammer force has no anti air option. Now there aren't many options that could keep up with the hammer force, and the stand out candidate is the storm talon. It's automatically kitted out with twin assault cannons, with four options for secondary weapons. The most effective option for taking on flyers would be the lascannons, but that's not much help if my opponent leaves the fliers at home. Consequently, if I take the typhoon missile launcher, I've still got 2 strength 8 shots, plus some redundancy through the frag missile option for taking on infantry.
Fast Attack 1 - Storm Talon
typhoon missile launcher
The hammer force also seems to be a bit light on assault ability, so I want to flesh that out a bit.
This next choice is a bit indulgent, and those of you who like being points efficient should probably look away now.
Elites 1 - Centurion assault squad
Land raider dedicated transport.
Like I said. Indulgent. But let's be honest, read the fluff for the centurions and its obvious that they are only used in special circumstances, so against an opponent with some high toughness elite units like dreadnoughts, terminators, or someone that's bringing fortifications, it's perfectly reasonable to suggest that some assault specialists would be equipped with the centurion suits. Clearly if you see three suits like that heading for you, you're going to pour lots of fire into it, so in comes the land raider to give them a bit of protection, it also brings plenty to the party on its own through serious firepower.
As a slightly more cost effective option, and to be used in less massive games, I always like to take a unit of assault marines. They may not rule the tabletop in this edition, but their speed and abilities means that they're very useful for tying up those pesky shooting units hiding away in cover.
Fast attack 2 - Assault squad
5 additional marines, veteran sergeant with power fist.
The final addition then to the hammer force is to add in more anti tank, mainly for use when I think an opponent is going to go armour or fortification heavy on me.
Fast attack 3 - Attack bike squad
2 additional bikes, all 3 with multi meltas.
Next then I want to give my opponent a few problems to think about to prevent them from focussing entirely on the two elements. First off, I want something that can reach out and touch from anywhere and potentially mess up my opponent's strategy, and for 65 points a whirlwind really fits the bill, causing pinning tests (I'm terrible at passing pinning tests, and I'd love to spread the pain to others!)
The next spanner to throw in the works is to give my opponent something to think about to prevent them from advancing on me in the first place. A maxed sternguard unit in a drop pod sounds like the perfect unit for that job, and no opponent is particularly likely to want that sitting near their deployment zone on turn 1, no matter how much firepower they've brought.
Elites 2 - Sternguard
5 additional marines, 2 heavy flamers, drop pod
Added to that, and for those armies that bring more firepower, I do like to include some terminators in my marine lists.
Elites 3 - Terminator squad
5 additional marines, 2 assault cannons
The problem with using the sternguard as a distraction, as I've hinted at, is that one squad can quite easily disappear against some armies, so in order to beef up the threat level, I need to have at least three drop pod units to guarantee two arriving on turn one, so in come two tactical squads
Troops 4 & 5 - Tactical Squads
5 additional marines, flamer, teleport homer and drop pod
The finally I want a fast objective grabber, so in comes a scout squad in a land speeder storm.
Troops 6 - Scout squad
Camp cloaks, shotguns, teleport homer, land speeder storm.
So there you have it, just over 3500 points worth of marines in a list that I have to say I'm pretty pleased with. Add in the imperial fists chapter tactics and my shooting becomes more reliable and tanks and fortifications are really going to be worried.