Mass Effect 2

When you reach the point in the Freedom's Progress mission where you are told to place your teammates around the giant blast door, you can trick the game into spawning extra YMIR Mechs (Ed: But why would you want to ... ?). First, position your team accordingly, and watch the cutscene. You'll now be confronted by a Giant YMIR Mech. Instead of killing it, turn around, and head BACK through the blast door. This will glitch the game back before the cutscene. Place your team around the blast door again, and the cutscene will play. This will spawn an extra YMIR Mech. Repeat as many times as you wish, but more than three YMIR Mechs will most likely kill you!

The achievement for gaining the loyalty of the theif.

Approach Legion in his quarters. Highlight him, but do not talk to him and he will eventually do the "Robot" dance.

Take Legion to the Citadel. Talk to Anderson and the customs officer.
Take Legion to the migrate fleet on Tali's Loyalty mission. Security will force you to remove him unless you can persuade them otherwise.
Take Legoin to recruit Tali. She will try to shoot him.

Notice after you press Y, the planet information screen on the right will tell you if the scan of planet reveals if it is "Rich", "Moderate", or "Poor". Rich planets typically give about 10+ good scan for ores. Ore yields vary from 1,500 to 3,000. Moderate will give about 8+ good scans, but around 35% to 55% yield compared to rich planets. Poor will give 5+ scans with yields 5% to 25% compared to rich planets. Note: If there is an anomaly on the planet (usually a rich planet) and you land before you scan, typically the Star Map on the Normandy will put you in a strange location away from the anomaly planet. Go back and rescan to get your ores.

Have a saved game file from the original Mass Effect and use that profile in Mass Effect 2 to get the following bonuses.

100,000 credits: Mass Effect character with the "Rich" achievement.
2,000 experience points: Level 50 Mass Effect character.
30,000 credits: Level 50 Mass Effect character.
5,000 of each resource: Level 50 Mass Effect character.
4,000 experience points: Level 60 Mass Effect character.
50,000 credits: Level 60 Mass Effect character.
10,000 of each resource: Level 60 Mass Effect character.

Fire the M-920 Cain and keep [Fire] held while pressing [Reload] after each shot. The shots will keep firing during the previous shots' explosions.

While recruiting Tali on Haestrom, direct sunlight will damage you and your squad's shields and Biotic barriers. Because Grunt uses armor, he is unaffected by the sunlight and does not suffer weakened defenses while directly exposed.

To find easy mining planets, go to the Micah system in the Vallhallan Threshold. Look for the three planets hidden in the asteroids. They are all "Rich" planets with a lot of materials to help with upgrades.