I have several go to cookbooks that are seasonally arranged and the recipes I know in general take less than an hour to prepare. In my case they are also vegetarian. One is Fresh Food Fast, which I love, love, love and have made close to everything in it at least once. Its organized around meals of two, sometimes three dishes, and is complete with a shopping list. The other is A Year In a Vegetarian Kitchen, which is single dish based but is pretty consistent in the time it takes to pull together. I've made perhaps half the recipes in this book (again way more than most cookbooks I own). The cookbooks aren't really necessary for my meal planning, but having an easy goto source of recipes is helpful for getting started.
So my system is to come up with a meals ahead of time, organized by the four-seasons and then list the ingredients it requires - all this information is on a 4x6 card (3x5 is too small for my sloppy handwriting). Sorta simple when I type it out. The meal usually consists of two dishes, sometimes one entree and a "Vegy Du Jour" entry (for something simple for whatever is in season - such as steamed brocoli or corn on the cob) or "salad". I think if you were an omnivore it could be even simpler since it seems like an easy fall back system is for meals tend to be organized around a meat dish in the vein of start with a meat, modify it (lemon chicken? roasted rack of lamb?), then add some vegetables. Vegetarian meal planning tends towards ethnic cuisine which doesn't lend itself to such straightforward thinking (more like what kind of stir fry or what sort dish complements squash tamales). But I digress.
To get meal ideas, I usually peruse my cookbooks until I find one dish I want to try and then consider what would go good with a "baked goat cheese, tomato and pesto salad", for example, and making sure it fits within the season and that the two or three dishes I'm thinking about don't take forever to prepare. I'll put the dish names at the top and list which cookbook and page number I can find them at. Or sometimes just put HM for home made. The cards are color coded by the four season (or are on their way to getting color coded - this is a work in progress!). I'll then list the ingredients that it requires in shopping list format, usually lumped together by "produce", "dairy", and "pantry". Sometimes I list staples (soy sauce?) and sometimes I don't (come on, I always have salt around!). After I've made the meal, I like to put comments on the back although, honestly, I don't usually get around to it as much as I would like. From year to year, I usually remember that we like something but not how much we like it. Like the dishes where I wrote that they were "insanely good". Its always good to read that! Some meals are duds and I try to cull those from the stack. If something takes too long to whip up - kiss of death for this household.
I've been pulling together meal ideas for about the last 3 years, so my pile of meal ideas is finally getting substantial, although I still run out of menus before the season is up. Making the meal cards does take some work at first, but then I don't have to reinvent the wheel next year. Its so nice to sit down on Sunday afternoon grab my green summer index cards and pick out 4 or so meals to have for the week, look at the ingredients list, cross check it with what's coming in my produce basket for the week from my CSA and make up my shopping list for Monday morning. I then leave the cards in my kitchen (paper clipped and stuck to the fridge) ready for me to start cooking. The other 3 nights of the week I usually leave open to chance - either left overs, take out, or I'll pencil in something that doesn't require any thinking like tacos or pizza. The setup is a work in progress. Usually towards the middle or end of the season, I'm starting to run out of good menus but there is still plenty of that seasons' produce still in the markets. So I keep adding new menus and culling the duds and it's working out pretty well for us.