I always like home-cooked best. Lasagna does seem like a "new baby" classic. Veggie lasagna is nice - lighter for summer, with lots of zucchini and bell peppers - yummy! I like the enchilada tray idea, too.
We have also made chicken parmesan for a similar one-dish gift. Make a coating out of bread crumbs, italian seasonings, and parmesan cheese. Dip boneless chicken into a bowl of milk (with egg if you like a thicker breading) and then roll in crumb mixture. Cook in a big nonstick skillet on top of the stove, browning both sides. Don't overcook or the chicken will get tough. Right before it's done, put a dollop of spaghetti sauce and mozzarella cheese on top of each piece, cover for minute to melt cheese.
I packaged the chicken and a marinade separately (in case anyone doesn't eat meat). Also include cooked pasta of your choice (bigger noodles like mostaciolli seem better for reheating.)
It also might be cool to do a soup - I just bookmarked this one from the NYT to try this week because it seems nice and seasonal: http://bitten.blogs.nytimes.com/2009/06/11/featured-recip...