Low Spec Games

Don't Starve, Rogue Legacy, and Super Meat Boy are good games.

X-COM: UFO Defense
Ys I&II
Uplink
Rollercoaster Tycoon

By the way, can you post a Speccy screenshot for people to know requirements they should stick to while recommending games?

Cthulhu saves the world

binding of isaac rebirth

Space Chem, FTL: Advanced Edition, Binding of Isaac

Point and Click adventure games and those Anime style novella games seem to have low system requirements too.

Fortix ?

The Walking Dead by Telltale
or The Wolf Among Us
or The Game of Thrones Game by telltale

Crysis 3 all the way

Games that I'm currently playing:
Killing Floor
Uplink
Airmech
Audiosurf
CS:S
Fork Parker's Holiday Profit Hike(just came out on Steam for free, it's fun)
LoL(some people love it, others hate it, but the minimum specs are lower than DOTA2, which it's good for me)
Monaco
One Way Heroics
Risk of Rain
Super Hexagon
Teleglitch
Hammerwatch
Mark of the Ninja(not playing anymore because I beat it, but still fun SP game)
Terraria
Bastion
HL2
Portal...

All I can think of right now. Have fun.

EDIT:
The lowest specs of all:
Cave Story+
Organ Trail: Director's Cut

AoE II + Forgotten Expansion , The Stronghold Collection, and Metal Slug 3 (are low spec and my favourites :)) )

I have an absolute toaster, but I ran Legend of grimrock and Fallout NV without mayor issues.

Also:

AI war
Tales of maj´eyal
Risk of rain
Hotline miami

Also the classics like deus ex-thief-system shock 2

Depends on exactly what you mean by low, but here are some good ones that a computer from 2005 should be able to run:
The blackwell series
Broken Sword 1 & 2
Conquest of Elysium 3
Darwinia
Delve Deeper
Dominions 3 or 4
DOOM 1 & 2
Eversion
Geneforge series
Half-Life
Majesty Gold (HD?)
Quake 1 & 2
Shadow Warrior Classic
Time Gentlemen, Please! & Ben There, Dan That!
Dawn of War 1
Age of Wonders 1 & 2

evil genius and overlord if u want interesting gameplay and good humor

Civilization Beyond H run good in low settings with 1ghz and 4gb of ram

Portal 2 ,killing floor,tf,csgo,L4D1,and all source games run good with the same spec but u need paste this in the launcher options,
-novid -high -dxlevel 81 -heapsize 2097152 -console (Not all maps run very good,but cache,inferno,and the new maps of the current op runs very good.

Need for speed Most wanted and lego gamesm,S.T.A.L.K.E.R Shadow of chernobyl,Rome Total War,Project Zomboid,Medieval 2 Total War,Tomb Raider games(Except the last TR 2013)Zombie Bowl O-rama.TWD1-TWD2, Fallout New vegas run good too but you need be patient with the fps 20 or 25 maybe is playable,Age of Mythology,Deadlight,Dragon Age Origins Ultimate ED,Half Life 1,Men of War,CoD1 and 2,

How low does it have to be?... You can try very good games:

Hitman 2 and Hitman Contracts and Hitman Blood money.
Psychonauts
Beyond good and Evil
Silent Hill 2 and 3
Indigo Prophecy
Mafia

Elder Scrolls IV: Oblivion,
Bioshock 1-2,
FTL,
Telltale games,
Bastion,
Cave Story+,
CIV IV,
Dragon Age Origins,
Fallout series,
Age of empires II HD,
Age of Mythology HD

Chrono Trigger, Zelda games, EarthBound

• LucasArts
• Talltale: Sam & Max, Monkey Island, Puzzle Agent, ...
• Spiderweb Software
• Daedalic Entertainment
• Pendulo Studios
• Wadjet Eye Games

• Fallout Classic Collection
• Sid Meier's Civilization® III Complete
• Sid Meier's Civilization IV: The Complete Edition
• Cave Story+
• Braid
• Cogs
• Broken Sword saga
• Half-Life 1 & 2
• Portal
• Cthulhu Saves the World & Breath of Death VII Double Pack
• King's Quest™ Collection
• Railroad Tycoon Collection

Satazius, 100% Orange Juice, Eryi's Action, Gunhound EX, Commandos 1-3, DESPERADOS, Original War, Earth 2140-60, Patrician, Tropico 1-2, Civ 3, Kof98, One Way Heroics...

I generally play Planescape: Torment on my Netbook during such times. Not on Steam, though.

Torchlight (both)

High five! I'm on my netbook during this Christmas time, so I feel your pain. I installed mostly some little games, just to spend the time I've got on my hands and get some achievements. The examples are:

Atom Zombie Smasher

Bejeweled 3 (surprisingly addictive one)

Botanicula

Don't Starve

Dead Pixels

Dungeons of Dredmor

Eryi's Action

Hero Siege

OMG Zombies!

Poof

Robin Hood

Super Puzzle Platformer Deluxe

Terraria & Torchlight (not a fan, but they're good for bad comps)

Geez why are you recommending The Binding of Isaac ??? This game and the ones like it are based on Flash which nowadays runs like SH*T on single-core processors......

don't forget diablo II

Death Spank 1 & 2