tj

http://www.bestgreenhometips.com/wp-content/uploads/2009/06/make-your-own-planters.jpg

I guess that whether or not a plant will be happy in this sized container depends on the soil used [regular garden soil will probably not work] -- how much sun/shade/heat the plants will get.[indoor/outdoor?] -- how long you expect to hold them in that sized container [annuals probably better suited than perennials] -- But, having raised all these questions ... one of the great joys of gardening is to push the envelope and experiment to see what works and what doesn't -- either way you win in greater knowledge --':)'

If you're going for flowers, may I suggest Lobelia? The most wonderful shade of blue and so cheerful ....more a spring flower in hot climate. Another easy to grow is Sweet Alyssum .... smell just wonderful. I have them growing in tiny nooks and crannies in my garden and they seem to thrive on neglect.... I'm trying to think of a veggie that will be happy in a smallish container ... bush beans [one] maybe. Might be fun to try and nothing beats picking a small green bean and eating raw. .... anyway, hope this helps you .... good luck in your 'tin-can-farm'

Yes, just about any annual bedding plant would work. If your part of Texas is hot you would need to water more than once a day. May need to paint the cans white so as not to bake the soil. If used in the shade, they may be a lot less work to maintain.

tj

May I suggest the Container Gardening forum?
http://forums2.gardenweb.com/forums/contain/
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CONTAINER SOILS
http://forums2.gardenweb.com/forums/load/contain/msg0715434425632.html?117
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tj is right ... you will be a slave to contant watering unless you can rig up some kind of tray under each/all of the planters to conserve water.
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Your motive to re-use is good. But I think that cans are among the easiest/most practical for recylers to make money on. You might want to look for recycled wood containers or even recycled plastic in a larger size ... many with a built-in watering tray.
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anyway .... have fun! Being a steward of our earth should be fun, whatever else it is. :)