The thing with trying to predict what space combat might look like is that we don't have a bloody idea

It's like a bunch of guys in 1890s trying to predict what air combat might look like in the 2000s. I am sure there were one or two visionaries who got the basic variables right, but the thousands of others were totally wrong (imagining huge flying fortresses and air cruisers and whatnot, their imagination clearly influenced by the experiences with naval war).
Now we're trying to imagine what war in space might look like based on our experiences with naval and air war. I am sure we're equally wrong - we can't even with any certainty say anything about the three main components of any war machine's power - mobility, armament, armour.
So it's all conjecture and guessing, and I am loathe to argue too much about it because personal (aesthetic) preference plays a huge role. Anyway, a few comments:
@ Cutlass:
When I said manoeuvrability, I meant evasion at extreme range. If you're hurling slugs of metals at each other separated by tens of thousands of kilometres of space, even with relatively low-g acceleration you can simply avoid most hits. This is of course entirely useless against speed-of-light lasers and near-speed-of-light particle beams.
In the end, perhaps the opposite will be the case and ships will simply be heavy behemoths with layers and layers of ablative armour, slugging it out with heavy beam weapons, kind of like the battleships of old.
As for your atomium-shaped ship, I don't really see the point. If the parts are redundant, why have them connected - you can have a swarm of smaller ships instead of one flimsy space-molecule.
@ hobbsyoyo:
Yes, mobility is a huge problem in "realistic" sci-fi. The way I see it, most "battles" will be fought near something of strategic value, not in deep space in the middle of nowhere (literally).
So, let's be cheesy. An American fleet is approaching the Chinese colony of Mars with the intent of capturing it for the American empire. What are the Chinese admiral's options?
-> He can lie at anchor at Deimos and wait until the Americans approach. They are the ones who need to make a burn to enter orbit around the planet. This will put them in range of the orbital defence installations and the huge planetoid fortress of Phobos, which will multiply the offensive force of the Chinese fleet.
-> On the other hand, they will get an opportunity to launch dropships to the surface and start dropping nukes on the surface installations. Even if they lose, they can cause an irreparable damage to the colony. Ergo, it might be preferable to burn and enter a very elliptical orbit around Mars and intercept the American fleet a few light-seconds away from the planet. But that carries a VERY significant risk. The two fleets will only fly past each other once; there won't be time to intercept it again before it reaches the planet. Thus, the Chinese must be sure they are strong enough to destroy or severely maul the American fleet in order for the remnants to be taken out by orbital defences. Losing the intercept battle (or more embarrassingly, failing to intercept the enemy fleet) means leaving the colony at the mercy of the victorious American fleet.
-> Worst of all, the Americans KNOW this and have probably planned accordingly for all eventualities.
As for detection, I think a combination of passive sensors, detecting the enemy ships' heat against the cold background of space, and active radar/lidars used for precision targeting will be used. The latter can of course be jammed, and the former "blinded". In essence, passive sensors in space need to be very sensitive to pick up the enemy millions of kilometres away - so why not, once you're close enough, flash them with infrared lasers and such to just burn their cameras? At the very least, it forces the enemy to close his "passive eyes", and rely on active—jammable—sensors. Sensor drones would of course be used heavily, I can imagine massive clouds of them reaching hundreds of thousands of kilometres in diameter deployed around the fleet of combat vessels. OTOH, speed of light comms delay means that further out, their utility in combat rapidly decreases.
A battle in space will be huge, huge mess. Non-stop jamming, drones and decoy targets everywhere, thousands of projectiles and anti-projectiles flying and colliding across the battlespace, lasers flashing, pure chaos. I love it
(BTW, the codex entries in Mass Effect 1 concerning space combat were excellent. It of course suits the ME universe where fleets can always disengage by entering FTL, but it is a really decent source of inspiration for me. Too bad the next two sequels ignored it.)
@ Ajidica:
There are many problems with lasers. One is the loss of coherence over distance (unless you use something like X-ray lasers or similarly infernal devices), the other is getting rid of waste heat and managing the degradation of your projector devices (mirrors etc.). This is why I don't like them very much. In my sci-fi setting, they are still a weapon deployed by all the principal races, but more in a secondary role - for blinding the enemy sensors and picking out point defence guns beyond their range so that smaller attack fighters/bombers have a decent chance of success.
As for AI - as I said to Hobbs above, I believe a space battle will be extremely chaotic. Thousands of things happening at once, and happening fast. It is impossible for a human to manage without advanced AIs taking care of things like picking targets, sorting them, and assigning guns to fire at them. Humans would be there to make principal decisions and to prioritize, but the "trivialities" of the combat would be handled almost exclusively by computers. The fact that communications between ships would be less-than-reliable in an all out battle only makes the need for independent AIs more pressing.
And yeah, we should make sure these AIs do not have a penchant for producing hot humanoid androids and wiping out humanity ("because that's a man's job!")
@ Michkov:
I was perhaps too general in that statement. I agree with most of their conclusions, but some seem too "authoritative" (meaning "authoritarian") for my taste. It's one thing to provide facts and calculations, another to say "and this makes this and that completely impossible, so forget it". While they might be right in many things, sometimes it's a bit too assertive. I won't give you specific examples now, because I read most of the things there years ago and don't remember exactly. I think the issue with "stealth in space" was one where I cringed. Sure, there is not "Stealth" as in "Romulan warbird" (aka "space submarine"), but there surely are ways to severely reduce your combat vessels signature and make it harder to spot
if you don't know where to look.
(I apologize for the tons of typos and grammar mistakes I surely made in this post, but I am too lazy to proofread it)