I want to spend money but I don't know what to buy!

Portal and Portal 2 for cool, tricky logic games. Only $5 for both now.

Endless Legend is awesome.

this :
http://store.steampowered.com/app/239140

the bridge Steam Link
a great puzzle in style of mc escher

Qbeh-1: The Atlas Cube Steam Link
relexing cube-puzzle game in firstperson

http://store.steampowered.com/app/233450/

A hand weight for power!!

Osmos and Eufloria are relaxing.

try Mr. Robot or Gunpoint

Skip the games and buy your mother a card and a nice bouquet of flowers. Bonus points if you make the card yourself.

Once that's taken care of, you might try School Bus Fun. That fulfills all of your listed requirements. If you're not keen on that, however, here are some others you might consider:

• Kami
• Ilamentia
• Never Alone
• Invisible, Inc.
• The Sun and Moon
• Dream
• Mind: Path to Thalamus
• Letter Quest
• TRI: Of Friendship and Madness
• The Talos Principle

Hotline Miami,Shadow Warrior,How to Surive,Battleblock Theater,CS GO(yes an must have),Valve games(complete pack for cheaper ones),and possibly other games you want.

don't spent it now, whait until you like some thing because you will regret it later

Desktop Dungeons

Play Solar Flux ?

+1 Antichamber

+1 Kami

+1 Qbeh-1

Checkout Hexcells and Lyne, both infinite, meaning you have new levels everyday or randomly generated.

Also, do you know/like puzzle platformers? Farming? Rythm? Tower Defense? There are lots of things to play :)

Do something kind this Christmas.

Buy 20 copies of Bad Rats and give them away here.

DYAD is 90% off, it's like $1.50. Watch the trailer and see if it's for you.

A Story About My Uncle is also on sale for 75% off, making it $3.50 - fun game.

Child of light is a simple game, but fun. At least if you liked fairy tales as a child.

Personally I bought multiple copies of portal 2 and sanctum 2 for friends.

Evil genious and Overlord Complete(3games) on GMG are 75 % without coupon and with it are cheap as pack of smokes.