Look into lasagna gardening. You'll find making lasagna beds a breeze--no work compared to removing acres of sod. And the soil you end up with will be greatly improved.

I usually hand dig my garden beds, and I've never removed any of the existing soil just amended it.
I'd kill all the grass and weeds first. Spray them at least twice with a week in between to be sure everything is dead, or you'll be struggling with grass regrowing in the garden for years.
If the area is large you might want to rent/borrow a small tiller to break things up.

I second laceyvail's suggestion to make lasagna beds.

When I did mine, the only digging I did was around the edges of the beds, throwing the clumps of sod into the new bed area. I used both cardboard & newspaper (in different areas) as a first layer and found that cardboard disintegrates faster than newspaper. Both did a good job of killing the grass under them ... except for some bermuda grass that grew through everything I layered over it.

If you have anything horribly invasive growing, I'd kill it first. Otherwise, it's probably not necessary.

That is ... not necessary if you're using the lasagna method.

Thanks! I'm tempted to rototill because, well, it's fun to tear stuff up. But I think I will give lasagna gardening a try. The thing is, I have a large area, and the process calls for a lot of organic material to go on top of some of the layers and I'm not sure where I'm going to find that much matter. Anyone have any suggestions on that topic?

Tree people usually produce more mulch than they know what to do with.
Check your local craigslist for sources too.

KarinL

I believe that Lasagna gardeners use their own "greens" i.e. kitchen scraps/spoiled onions, potatoes etc and also haunt their local food markets for theirs. Similarly, Starbucks for coffee grounds.