Ezra Klein has a good recipe up for the process of slow roasting tomatoes. What's most interesting about it is that it uses canned tomatoes, which I've never seen... and provides an interesting culinary opportunity in the winter months. We're currently in the process of slow roasting our own tomatoes... small cherry ones from Anna's family house up in Maine. I use Alton Brown's recipe, which involves a much lower oven temp (170-200), a longer roasting period (8 hours for plum tomatoes - the cherry ones only take 3-4), probably some more salt and sugar and less oil, and fresh thyme instead of dried oregano. (I'll add the full recipe once I have access to the book)
The tomatoes themselves are awesome, and are great on bread or whatever, but also make a fantastic soup (and presumably a great sauce too). We're going to make that soup this week or next, so I'll be sure to blog it.
It's a great thing to do to excess garden tomatoes (not bigger than plum though) because they last for at least a month in the fridge and can easily be frozen for ages.