Opening scene of original Star Wars. Not a huge battle as it was only one ship going after just one other. But it was spectacular.

I remember the first time I saw it.

I wondered if that ship had an end as it kept on coming and coming.

Forester, yes exactly, it was such a great piece of film making showing the dramatic difference in scale!

I immediately thought about the opener for Star Wars.  It established scale like few space scenes achieve.  I got to see it in LA during the first week.  Nobody had any clues yet what was in that movie.  So, without any warning from previous movie effects, the emotional impact of that huge ship was amazing. I had been doing the whole stand-in-line-around-the-block thing and in those few seconds I knew it had all been worthwhile.

I find myself strangely unable to come up with non Star Wars space battles that conjure big memories.  I am interested to see what examples people offer.  All I come up with is an image of a Borg ship sweeping across the screen.  I was impressed with Borg ships as example of non-Terran, non-aerodynamic space ship design.  They just struck me as really mean.

First fight in BattleStar Galactica looked great to me. I think the reason is you have superheavy carriers lobbing missiles at each other and the fighters duking it out in the middle. It just gets incredibly intense and still looks stunning, both up close and far away.

Also final simulation in Ender's game, heavy spoilers obviously. I like this because it does a great job at integrating the running plot with the battle. It's not just a bunch of raggedy-run pilots screaming at each other.

Emotion-wise I have to go with the freespace open trailer. It's the only one where I feel I get "sucked in" to what I'm viewing. Just great voice-acting, the radio chatter feels real.

Babylon 5 - Severed Dreams.  They did a great job with the setup, so you actually cared about some of the characters involved.  Hiroshi's big moment presses the appropriate buttons/chokes you up.

I particularly appreciate the B5 Space FX work as they pay better attention to Newtonian physics with their designs.  Some of the other battles in B5 are really cool as well.  However, Severed Dreams is my go to B5 battle.

The 'newer' Battlestar Galactica also deserves Kudos on the Newtonian end, and yes they've had some good stuff as well (with better CG templates to boot).  It's nice to know that SOME Hollywood FX people care about space movement physics... Aerial style dogfighting doesn't work if you don't have 'atmosphere' to push your flight surfaces against...

Hands down, the space battle over Endor.

I have yet to see something beat Star Wars VI, the Battle of Endor in terms of full battle sequence. I even have a cut version so that I can just watch the entire space battle without going over to the other two plots taking place. (heh...on youtube as well)

Number 2 for me definately goes to Serenity: "Somebody FIRE!". Jam-packed full of action with "I am a leaf on the wind" guiding the screen capture. Love it.

I had high hopes for the Star Wars III opening sequence but in the end turned out to be a huge let down for me. Don't get me wrong; it was visually stunning without a doubt and I was totally psyic'd to see such a splay of destruction. However, I find it really falls short once its zooms to the inside of Anakin's cockpit as the screen tries to capture his emotion in a very emotionless way. and buzz droids?!? Yeah....that ends the movie for me right there.

Did the soundtrack in the first video in Hf's post make anyone else reminisce about the original Transformers movie?

Anyways..

It's tough to top Star Wars, but Robotech (especially "Blitzkrieg") comes in as a close second for me:

Gotta vouch for Battlestar Galactica, probably either storming new caprica or battle of the asteroid...

Well I guess I can cover Star Trek- 

(you could play Star Trek Armada 3 too haha ) 

When the Borg come you better throw everything you got at it and and yes Sovereign is a sexy and deadly beast.

Good choices folks! 

I second the B5 "Severed Dreams" fight - the political intrigue and plot development surrounding the battle made it feel way more epic and imo compensated for the somewhat lesser graphics.

Space Battleship Yamato.. Both the anime, and live action movie. Battle near pluto (or mars in the LAM).

Space: Above and Beyond and especially this: 

And not in space, but never skipped when I played...

Mech Warrior 2 Intro: