I like to plan out my vegetable garden early, so I know exactly which vegetables & herbs I want as well as which specific varieties. Burpee Seeds has an article on companion planting – plants which deter mutually beneficial or harmful insects, etc. I pull out my gardening books, scout through them & make decisions at this time of year so that I may go to the store early in the year to buy the seeds I want from a local gardening center. Later on, it is also possible to return for starter plants, because some vegetables like cantaloupe (my favorite food of all time) are challenging to start & to grow in the garden. Last year I actually got fruit for the first time & it was the 3rd year I had made an attempt. Starter plants are more expensive really (you pay maybe $3-$5 for one plant when you can buy a packet of 20-150 seeds for that plant (depending on the size of the seed) for less than $3. It is more economical to start plants from seed, but it can be challenging to start some plants from seed in certain areas (the soil is too cold, too moist, not moist enough, etc.). This makes it worth buying a starter plants when needed if you usually start plants from seed.
Johnny Seeds (http://www.johnnyseeds.com) is a site recommended to me by a local farmer at the farmer’s market & a former coworker. It shows a variety of seeds & specifies some characteristics of each one – for example, how the tomato tastes, whether it has a more juicer or there is more flesh on the inside, shows different colors of tomatoes (did you know that there is a variety that is striped?), etc. It’s another place to go to check out varieties of seeds.