Look how many Gamerscore points you can amass with just an hour or two of Madden NFL 06 on your XBOX 360 (Got the point totals from J Allard's profile):

Get a First Down: 20 Points
Score a Touchdown: 30 Points
Rush for 200 Yards In a Game: 100 Points
Pass for 350 Yards In a Game: 100 Points
Amass Four Sacks In a Game: 100 Points
Win a Franchise Game: 100 Points (OMGSPLOSION!)
Complete an Offline Game: 30 Points

So, here's my advice for major points:
Rent Madden 06 or borrow it from a friend. Start a Franchise with the Buffalo Bills (your week 1 game will be against the Texans) on the lowest difficulty level. If you win, get a first down, rush for 200 yards (hey it's Willis McGahee against Houston's defense), and score a touchdown, you will amass 280 points. 280 points is almost double the amount of points from beating Call of Duty 2. I know I'm going to do this when I get a 360. So what do you guys think? Do you have any other suggestions for a large amount of Gamerscore points?