The closest thing I could find was damage from Banyel herbicide,

http://vegetablemdonline.ppath.cornell.edu/diagnostickeys/TomWlt/TomWiltKey.html#Banvel

http://vegetablemdonline.ppath.cornell.edu/diagnostickeys/TomWlt/Dicamba_Tom.htm

But I suspect that it might be something more like leaf edema occurring on young stem tissue rather than leaf rib.

http://vegetablemdonline.ppath.cornell.edu/diagnostickeys/TomLeaf/TomLeafKey.html#Edema

http://vegetablemdonline.ppath.cornell.edu/diagnostickeys/TomLeaf/Edema_Tom.htm

spiced ham- thanks so much for the response! I don't think there is any way that I have had any herbicide damage.

I can't find too similar of a picture with the leaf edema, but all of the descriptions seem to match up! We've certainly had some cool, humid, wet weather lately. That would be a relief (even WITH damage) to know it wouldn't be something harmful to be introducing to the soil. I really want to get these in the ground by this weekend!

Thanks for your response!

Doesn't look anything like Banvel damage. Nor does it look like edema as pictures at Cornell.

Possible for white spots is powdery mildew. Need to increase air circulation.

Beyond that, the plants need to be set deeply in larger pots,
need nitrogen,
and need lots more light.

Hey MeganSTL -- Did you ever figuure out what was going on with your seedlings? I have something very similar on my seedlings this year, too. First I thought it was edema, but now I think it might be bacterial canker -- which effects seedlings in similar ways. I don't know if I should throw out all my transplants (even the ones that are doing okay) just in case -- to avoid contaminating my garden. Any advice would be appreciated!

giddykitty, I had bacterial canker last year in purchased seedlings. It first appeared as a dark line of dead tissue along the edges of the leaves. Eventually there was some dark tissue inside the ribs and stems.

No pale or blistery spots, ever.

Please be aware that bacterial canker -- if that is what you have -- stays in the soil for 3 years, so don't compost your plants or the mix they're growing in. Clean the pots thoroughly.

I probably spread it from plant to plant on my hands or a pruning tool.

If you have it on your seedlings and never saw it in your garden before, you may have purchased infected seeds.

These are the best links I found:
http://vegetablemdonline.ppath.cornell.edu/factsheets/Tomato_Bacterial.htm
http://www.amseed.com/pdfs/DiseaseGuide-BCT-English.pdf

I am not a tomato expert, but geraniums (pelargoniams) get edema when they are in a cool greenhouse and cannot expire water quickly enough. They completely recover when put out into the warm sun. Can you put your plants out in the sun for about a week to see if they recover?

I didn't ever figure out what was on my tomatoes, but went ahead and put them all in the ground. I had two plants die on me last year (both Green Zebra plants), and everything else turned out completely fine once I put them in the ground. It was an incredibly hot summer, so I had some issues with lack of pollination come July, but overall, they were safe as they were to be put in the garden (as far as I know anyway!). Hope that helps!

Here is a link that might be useful: Megan's Messy Garden