What's Wrong With My Tomato Plants?

[Decado]

Went out to the garden today and realized that several of my plants have been completely taken over by this:
[img]https://i3.photobucket.com/albums/y69/wrathloki/7-16-2009/DSC01956.jpg[/img]
What is this?

[rainbowgardener]

Very hard to tell from the picture. Try again with more pictures of the plant and more information about what conditions it's growing in and what your weather's been like.

[Decado]

If you notice on the edges of the leaves, completely around the whole leaf, they're turning black. Then there's also yellow spotting on the whole leaf. It's getting worse, taking over the whole plants. The day I took this picture was the first of about a week of 65-75 highs but before that it was normal summer 80's-90's, the leaves were starting to get this before we had the 65 high days. We've had pretty much no rain all spring and all summer (mowed the lawn 3 times so far since winter) so I'm watering about 3 times a week in the AM. They're planted in fairly sandy soil but we covered the garden in about 4 inches of composted manure and tilled it in this spring (which made stuff grow like crazy). I'll get some more pictures but does this info help at all?