Seeing as I use my Xbox almost exclusively for "single television multiplayer" these days I couldn't help but post my opinion here (hopefully not every disagrees with me and my friends. lol).
Now, Guitar Hero: World Tour (or any variety of rock band, etc) is fantastic as long as you can find someone willing to sing, although it's certainly not cheap if you are buying it in Australia.
Marvel: Ultimate Alliance is a fun little game that you could probably get really cheap these days and my friends and I have a blast with it. Game leaves a lot to be desired single player unless you're a huge Marvel fan boy but multiplayer (arcade mode specifically) is a hell of a lot of fun. Very "Gauntlet" style gameplay with a lot of variety of character choices, especially if you like the downloadable content option on your 360.
If you DO play a lot of single player, there is a lot of fun multiplayer in Soul Caliber 4 if you've done your homework. Go out of your way to unlock all the gear for "Special Versus" characters and have all your mates come over and make characters. Ads a lot more fun to the standard "Ryu vs Ken" style fighting games and fills you with a great sense of pride when they start calling {your characters name} cheesy and over powered instead of the character's moveset you based it on.
If you're just after a laugh, you could all start a brand new game of Grand Theft Auto 4 and take it in turns trying to see how long you can survive when trying to get to the third island before you even do the first mission. Added humour value to an already great game. lol