The best "weed" control I have used is mulch. I have not seen any "weed" spray that actually works and they are usually very expensive to use. Mulches not only will aid in suppressing "weed" growth bit also aid in maintaining soil moisture levels and will add the important organic matter that is so necessary to good, healthy soil. Mulches will also aid in lowering your soil temperatures so even less soil moisture, evaporated to aid in cooling, will be lost.
The few "weeds" (unwanted plants growing where I don't want them) that I do find are very easily hand pulled in the well mulched planting beds.

You are using one piece of the weed control arsenal. Spraying with Round-up before planting does a good job of cleaning up the growing weeds, however it has no residual and your soil will contain a reservoir of weed seeds waiting to germinate after planting.

Commercial growers will use the same practice if they have growing weeds present before planting and tillage is undesirable or ineffective. However, after planting you will get a new crop of weeds to deal with. For this, commercial growers will use a number of tools. Cultivation, plastic mulches, selective herbicides, sometimes with residual control, and hand labor, all selected based on a number of variables. For the home garden, there are few good herbicide choices due to the nature of a typical garden. In a garden you generally have a wide variety of vegetables in a small area and most herbicides are selective--they will not hurt certain types of plants yet are devastating on others. In a garden, you rarely get enough area devoted to one type of plant to use a selective herbicide. Instead, your selective herbicide will get spread into susceptible veggies and take them out, too. In addition, application rates for herbicides can have a narrow range of tolerance. Just a little too much, and the herbicide will remain in the soil long enough next year to wipe out a bunch of your veggies. Not quite enough and it won't control your weeds. Unless you can use mechanization to ensure uniform application rates, you are playing russian roulette. A hand sprayer is terrible at getting a uniform application. It becomes a delicate juggling act which requires quite a bit of expertise to minimize costs, maximize weed control, prevent herbicide transport into water or other non-targeted areas and avoid damage to wildlife, match the herbicide with the weeds present, prevent herbicide residues from entering the food supply, rotating herbicides to prevent resistant plants from developing, etc. The average homeowner is not going to spend the time and money to gain the level of expertise to use the full arsenal of herbicides safely and effectively in a cropping system they weren't designed for.

After cleaning up the green weeds with Round-up before planting, then cultivation or mulching is probably the most common and effective tool in the home garden. If you can shield your garden plants, you can also use Round-up later in the garden for weed control just as long as treated weed foliage doesn't touch your desired plants until after the herbicide dries--use a shield to prevent spray drift, go after the weeds while very small and easy to kill, and stick with mulches, cultivation, and hand weeding.

Tilling the soil effectively kills "weeds" as well as any spray you need to buy, faster, since you need not wait for the spray to take affect, and tilling those "weeds" in adds some organic matter. Some times yo may have a "weed" that will grow back from the root, but you would have that problem with many sprays anyway, however once the garden is planted and then mulched properly "weeds" will be denied access to the sunlight they need to grow, so they don't.
Buying sprays to control "weeds" is usually a waste of your time, energy, and money since they usually are not needed.

Veggie gardening is not my thing but for a 20 x 100 bed I think a mixture of Kimmsr's and beeone's methods is just about right with my preference weighted a bit more towards Kimmsr's for the period after you have initially prepared the ground (although I confess to using RoundUp here and there even after initial prep.). The things big farmers use are as much trouble as help for anything less than an acre. Newspaper or cardboard covered with mulch should help. It also depends what weeds you are fighting so research and trial and error is needed to learn what works best on specific weeds in specific areas. In the off season, I would strongly consider a cover crop which can enrich soil and compete against weeds until planting time rolls around again. I am no expert but on a few occassions I had such great success using Rye Grain to control areas over the winter time that I am sold on the idea. A certain amount of weed invasion is also just the way it is so don't let it drive you crazy.