Actually I found you can keep on creating profiles with different email addresses (I don't remember if you need to say phone numbers but you can look some up in a phone book) and keep on getting 1 month trials. Of course you can't keep any friends lists or achievements or anything on that account.
Stay far away from Halo 2 though, the things people do on the lower levels (it's ranked) is disgusting.
It's awesome if you want to have an extra account for a sibling to play, I've only made 2 accounts though and both of them expired so I'm not sure if this can work over and over again. I think you need to start from the initial setup option under the system blade and say you want to create a new online account every time. I figure it's more worth it to buy Live considering all the games with multiplayer and the option to block idiots in most games.
