I am broke, 
Far beyond broke. I also, have been playing a fair amount of oddities this summer. With that in mind I thought I'd put together a list of some of free games you could be playing.  
 
GAMES,

spelunky

system shock  
n (the first game not N+ but, still a ninja game)

http://osu.ppy.sh/p/about

ikachan

cave story   
frozen bubble
 
Thanks to the GiantBomb user

louiedog I realized a grave error in not including Octodad and, 

Please if you enjoy it kick in a few bucks so part 2 can get made.

https://www.digipen.edu/gallery/games/

http://www.reloaded.org/index.php

http://www.abandonia.com

Digipen is filled with student projects. I couldn't tell you what is good or not in that but, There are a ton of little games. 
Reloaded and abandonia are filled with abandon ware and free ware games. Even though sometimes abandonia has a buy through link instead of a download link and,  both sites have games that can sometimes be a pain in the ass to get working with modern computers. 

http://projectorigin.warnerbros.com/fearcombat/main

http://www.gog.com/en/gamecard/beneath_a_steel_sky 
http://www.rockstargames.com/classics/?id=1  
I also forgot, you can get Back to the future episode 1 for free on telltales site
and, Wolfenstein: Enemy territory
there are also a few things on steam for free provided you want to have a steam account like Team fortress 2 and Trackmania.
I say free but, not free because you have to register them to use them but not a bad deal for a free game.   
 
Hope this list helps someone play something they will enjoy.
I will add a secondary note in here that if you enjoy any of the above games or any game for that matter please support those games in whatever way you see fit. 
Be that by money or simply sitting down and, Writing your favorite game makes a note. Working in the video game industry sometimes can blow. It's cool 
to know people like what you put your heart into.

I don't think those last ones are entirely legal. However, you're lucky in that for whatever reason, I can't flag that post. Hopefully, a mod will see this post and reset my karma.

Spelunky's awesome, what's not to like about a side scrolling roguelike?

I don't know if these are available somewhere in the depths of those sites but http://www.supercratebox.com/ is a fun little 2D action game and http://www.desktopdungeons.net/ is the bastard child of a puzzle game and a roguelike.

You can pay for a shinier version of DD but I spent quite a few hours with the freeware version.

ScummVM is a program that runs old adventure games, most notably those that were made with SCUMM (Monkey Island games, Maniac Mansion, etc.). While those more well known games cost money, there are also some adventure games that have gone freeware posted on the site. One of them is Beneath a Steel Sky which you've posted above, but you don't need to register to download from the ScummVM folks. You do, however, need to install ScummVM to play them. The others may be listed in some of the links you posted, but I thought I'd mention ScummVM because it makes them playable on large number of platforms, including phones. It also makes those old Adventure games very easy to run. There's no messing around with dosbox or fiddling with settings. Most games just work.

Games:
Beneath a Steel Sky 
Flight of the Amazon Queen
Lure of the Temptress
Drascula: The Vampire Strikes Back
 
http://scummvm.org/downloads/
 
I might as well also mention that Angry Birds is free to play using Google's Chrome browser. Grab it from the marketplace. On other platforms it's a paid or ad supported app.
 
edit: Oh, man. I just realized you missed Octodad! It's a student project and they currently have a kickstarter going to fund Octodad 2. Giant Bomb user Hamst3r did... well I guess you'd call it an Endurance Run here. It's crazy.

Is this game free? I'm a terrible person.

@louiedog:  I didn't so much skip Scumm_VM as much as I skipped it because some of the games fall into that grey area mentioned in the comments. the only I listed Steal Sky is because it's on GOG and it works with no tinkering. (or so I'm told. I played it years ago.)    I however did forget to mention octodad I'm going to link it above because that's a bit of a crime.

I'm a lifeguard its impossible for me to beat the summer heat.