Typically once planted in the ground or in a large pot, tomato plants will grow quickly. I usually see at least a foot's growth in the first few weeks, as well as a lot more branches.

If yours aren't growing very well, there are a few reasons this could be:

- It's too cold. Tomato plants are not fond of the cold and might not grow as well under those conditions.

- Not enough nutrients. Did you give the plant some kind of tomato food, fertilizer, etc when you planted it? Mine get a handful of long lasting granular fertilizer in the hole before I put in the plant.

- Using too much energy on buds/tomatoes. Did you pinch off any buds that popped up? It may seem crazy, but until your plant is a good size you should pinch off any buds that appear. This allows the plants to focus their energy on growing the plant instead of growing tomatoes. This will meant a healthier plant and more tomatoes later.

I planted my tomatoes in their pots on May 5th. I started growing them inside from seed at the beginning of March and then moved them outside a couple weeks before I planted them so they could harden off. 

Here's what they looked like the day I planted them:

   
(click for larger photo)

Here's a comparison of what they looked like on May 23 (when my husband helped me stake and mulch them) and today on June 1:

   
(click for larger photo)

And here are some plant to plant comparisons between May 23 and June 1:

As you can see from the photos, they grew both taller and bushier in just a few weeks. This even includes pruning some sucker branches and bottom branches off the plant in order to concentrate growth further up the plant.