This is an easy question, kinda. I would only put one type of input into source.list. So, if you want to upgrade to sarge, put sarge in there, not all of them. This will make it such that you don't end up updating and find that package x from sarge needs package y, but package y is from sid and breaks package x because it is not the exact one that the original package was built against. Be very cautious when going up (or down, there is an article on how to do so from debianplanet.org). You might have more frustration than you bargained for.
That said, check this link out. It has a few source.list entries that are useful. When I get around to it (probably later today), I'll post my current source.list. You can also check out pbharris' PET. It contains much useful information and some more source.list material. Don't forget Debian's website, as they have a tonne of great info.
BTW...welcome to the forum!