I like to till in the fall for this reason. In the spring, when the soil is warm enough, I plant out all my cool-season crops, rain or shine. It's very important to lay out pathways in the fall as well, so you're not walking all over the wet soil. Rain jacket, rain pants and rubber boots complete the picture :)

I often have the same problem. Here (in Northern Missouri) I have had success with simply placing the pots and plants all grouped together in the garden, self-supporting one another, and then actually transplant them into a permanent spot, even if muddy, when the weather breaks enough for me to plant them. Sometimes I can get only a few planted and have to run for shelter until the following day. I do try to give the soil around the newly planted plants some weed protection by laying down a few sheets of newspaper (around the plants) weighted down with some spare mud/soil. Good Luck!

I'm always pleased if it rains after transplanting. You water them when you plant, of course. But if it then rains afterwards that helps bed them in. Transplanting in warm, dry weather is a pain imo. Not that it happens much. Rain every day for 10 days is normal spring weather here.

I planted out lettuce the day before yesterday deliberately because it was between showers. I'd get those cool weather crops in asap, and hope for rain after.

So.... it's not too hard/stressful for the plants to get pelted with rain and totally soaked in their first day out? I don't care about getting wet when I'm out there planting, it's not like it will be continuous rain and I shouldn't need to step into the soil in the garden to do my planting (I have stepping stones/boards throughout the garden beds). I was just under the impression that the plants wouldn't transition well if they got inundated right at transplant time.

Thanks for the quick feedback... I'll plan to get those cool crops in this afternoon and the tomatoes this weekend as planned!

As long as you don't have standing, stagnant water sitting around after the rain ends, they should be fine. It's much less hard on the plants than being exposed to wind and sun. And as floral_uk pointed out, a nice rain drives out all the air pockets between the rootball and the soil so they establish quickly.