Besides lettuce and greens my favorite first early crops to plant are peas and carrots.
I tilled this weekend and put up a bamboo trellis for the peas much like the one shown above from organic gardening magazine. I use bamboo because it is strong and lasts and lasts and biodegradable twine because it rots making the contraption easy to rip apart when I rotate crops in the spring.
For carrots, I make sure the soil is well worked; no sticks and stones. I spread seed thinly in rows mixed with a few radish seeds as carrots germinate slowly and this reminds me of where they are. Don't forget to water them well or plant just before rain. Do not fertilize much and especially do not add manure as the carrots will fork. I plant lots and lots of carrots as these and potatoes keep well in our 45 degree damp basement.
Leftover potatoes or green potatoes from the basement storage we sprout each year in sunlight during the month of April in the enclosed porch and then cut up and plant. With greened up sprouts the potato plant is so much more productive and stronger. Last year, we had a fabulous crop of russets and reds. Yes, you can use store bought potatoes, although those from a farmer's market or farm store will probably not be sprayed with a growth inhibitor.
Now I'm back at the drafting table and content, as it will rain on my seeds tomorrow.