I think there is only one technology that I have researched in every game I have ever played without fail, regardless of my race, strategy, and start position.  That is the repair bay.  It is the tech to always research.

Aside from that (on the military side of things) you have the usual "vital" technologies regarding unit prototypes.  You need a balanced fleet, and usually that means LRF, carriers, flaks, and probably a support cruiser.  I personally am a huge fan of antimatter upgrades, but keep in mind I'm also love my capital ships, so I put those upgrades to good use.

For useless technologies on the military side, I'd have to say the Vasari technology that increases capital ship bombard range is probably the top candidate.  It's ridiculously expensive for something that has virtually no effect.  Not worth your time or money.  The capital ship beam weapons are another dubious research; at least they do something, however.

Now, the civic side of the tech tree doesn't have very many "must have" technologies.  I think ice and volcanic colonization are probably the most important in the long-run so you can claim those planets both as tactical staging points and for their resources.  As Swordsalmon already mentioned, the population upgrades are a great investment and the low-level extractor upgrades are well worth your time.

Now, I could probably rant all day about weak civic technologies, but let me address an absolutely worthless one: pirate xenophobia.  This ability reduces the strength of a pirate raid against you by about 10 or 20%.  An experienced player probably already knows what I'm about to say, but I'll say it anyways.  This pirate raid is still strong enough that I have to go back and fend it off.  If I go back and fend it off, then this upgrade has effectively given me 10 or 20% less experience for doing so.  In other words, this ugprade is actually a bad thing to have.  It's one thing to be a double-edged technology (TEC insurgency can feed the enemy experience in the long-run, but at least it has positive side effects), but this tech seems to literally be a detriment.

Those actually are pretty good.  Certainly not early-game technologies (cept the Advent one since it's available with 2-labs) but definitely worthwhile.

Situational but worthwhile if you do put them to use.

Not worthless, persay, but definitely overpriced for what you get.

actually extractor upgrades are the most important econ advancement on the vasari civic tree because they ahve to wait for 4 labs to get trade ports up. you can get 4 upgrades for extractors (both metal and crystal) with only 3 labs. If you run short on credits you can sell the metal or crystal at the black market.

_|~Uber

My quick list of techs that I find less than useful:

TEC:
    Combat:
        Capital turn-rate
        Beam damage
        Missile Range
        Cielo (Without researched ability)
    Defense:
        Gauss RoF/Range
    Civilian:
        Refinery
        Ice Pop
        Trade ship armor
        Cap training level
Advent:
    Combat:
        Beam range
        Cap training level
        Scout Kamikaze
    Defense:
        Hangar strikecraft
    Civilian:
        Multi constructor building
        Antimatter constructor/improvement
        Culture resistance
        Seeker vision upon death
        Resource Focus
        Bounty on enemy for killed tradeships
Vasari:
    Combat:
        Cap training level
        Overseer researched abilities
        Pulse Gun
        Pulse Beam
        Bombing Range
        Wave Cannon
        Armor boost+Mass decrease
    Defense:
        Grav mines
    Civilian:
        Salvage from dead enemy cap
        Refinery
        Nanite Jammer/improvement
        Bounty gained increase
        Pirate raid strength decrease
        Ice pop
        Capital culture suppression

The problem with gauss turret range and RoF isn't their power, but rather that people don't normally use gauss turrets

I don't see your aversion to the Vasari pulse gun.  It benefits the skirmisher and starbase and is cheap to research.  If you're using skirmishers (it does happen, for instance against carrier massers) this is a great one to have.

Well, of course if you're not using the unit-type the ugprade isn't worth researching.  That has nothing to do with the upgrade being bad or something to avoid.  If you are using skirmishers (and yes, I have done it quite a bit in multiplayer) then this upgrade is a shoe-in due to its low cost.

Do not research techs that you are not going to use.

I usually don't get Refineries. If only Refinery was cheaper to build by half I would get that tech every time.

kinda figured but the wording and context seemed to imply that you agreed that the Guass technology was worthless but that pulse gun technology was worthwhile though you gave the same reason for both which seemed contradictory

Kitkun,  I almost always watch replays and look to see what people research.  I would say:  there is very little concensus in what to research. 

The only essential techs on the civil tree are: ice & volcano, and maybe trade, and then maybe culture.  Nothing else is game changing early on.  (In fact, I've seen people scuttle their civic labs, after they get ice & volcano, and research nothing else there)!  Often, online players never even build civic labs, and rush to full military!  They just skip over the ice & volcano planets.  It kinda depends on how long the game goes, and where you are located on the map, in relation to your enemies.

On the military tree, only the various units, and repair are essential.  There is wide diversion among the armor, health, shield, and various weapon upgrades.  I think the vast majority err here, by spending too much money for the measly 5% improvements (when just buying one more unit is probably more cost effective).

Later, when I've got more time, I will give my lengthy list of 'worthless', or non essential techs.

Does any body use the reintegration ability on the skirmisher. to me it seems useless cuz if they need it they are probly in heated battle and will die anyway or the fights over and i rather use overseer or repair bay than wait for these ships to regain function.

It's also nice (though I mainly only use it on the enforcer) if you win a big battle and your enemy retreats to an unfortified planet. Sense the skirmishers and enforcers can heal themselves, you can use the overseers to heal the rest of your fleet and then give chase to your enemy much faster than any other faction. It's also nice defensively sense late game I only have a defense fleet of low level caps, sentienels, and skirmishers/enforcers that often have to immediately jump from one battle to the next via phase gates. Getting them to full hull points quickly can be the difference between a battle won and a battle lost.