I think my garden's first and best line of defense is the birds. I put out gray striped sunflower seeds, black oil sunflower seeds, and safflower seeds mix, a block of all weather suet, and a separate finch feeder of niger seeds. I don't use any herbicides or pesticides in the yard/garden. It's full winter here for us now, so I'm getting cardinals, blue jays, chickadees, titmice, downy wood peckers, red bellied wood peckers, nuthatches, goldfinches, and house finches, to name the primary visitors. I also get Carolina wrens and house sparrows during this time. On the ground (not to the feeder), there are flocks of mourning doves, junkos, white throated sparrows, and song sparrows, presumably eating grass and weed seeds.
In spring, the finches, chickadees, titmice, and woodpeckers will start eating the first aphids and other bugs from the branches, stems, and buds. They'll be joined by house wrens that start claiming and nesting in the nest boxes scattered all over the garden, and of course the robins come back too. As all the birds start nesting and they start feeding their babies, they literally clean up the bugs! (I had two infestations of tent caterpillars in the mulberry tree (ha!) and a plum tree last year -- I didn't have to do anything about them. Especially ones in the mulberry tree didn't have a chance, they were gone so quickly!) Summer time, the hummingbirds, occasional warblers, catbirds, mockingbirds, and yellow shafted flickers join in as well as other less frequent visitors like bluebirds, and let's not forget the starlings, blackbirds and grackles....
Of course offer bird baths too -- particularly welcome in freezing winter and hot summer. Running water like a fountain or waterfall attracts them even more in the warmer months. Some birds like to bath in shaded sheltered spot, others prefer to bath in the open.
Forgot to add -- another suggestion is to plant "insectary plants" -- plants that attract beneficial insects. One summer day last year I counted over a dozen species of predatory wasps and flies nectaring in the mint patch. There are other many other suitable plants -- do a search from the main index page -- I believe there were threads about beneficial insects in the Permaculture forum as well as the Organic Gardening forum. It's great that you already have ladybugs in your garden -- it's kind of hard but you have to let the aphid population build up
... enough to support the ladybugs, then the plentiful food supply will trigger them into reproducing. Last year, my plum trees were COVERED in aphids, then the ladybugs moved in, and we had to tiptoe around the trees so as not to accidentally squish the ladybug larvae and pupae that were EVERYWHERE and the aphids were history