Now is the perfect time of year to turn your sunny window into a seedling factory. Start with either new small pots or recycled pots that have been cleaned with soap and hot water. Also use brand new potting soil for seeds to prevent disease.
Plant seeds twice as deep as the seeds are wide and maintain moisture until you see germination. Allow for one plant per 1-2 square inches. You may need to move them to a larger pot if seedlings start to shade each other.
If your seedlings are stretching or leaning towards the light, then you should be increasing the light by moving the plants to a sunnier spot or placing the plants within a couple of inches of a regular cool white fluorescent light (no need for a grow light for seedlings).
By growing your own seedlings you can save a lot of money over purchasing plants later in spring. Also, you can select to grow seeds from a larger diversity of choices (i.e. early tomatoes, unusual varieties or heirlooms).