How long can I leave an uncooked steak out?

Even if you just pull them out for about 30 minutes once you get home that will be better than not letting sit out at all. The main benefit is that it will cook easier and you'll have a natural gradation from brown to pink on the inside rather than the gray color that often occurs. I myself don't typically pull meat out an hour before cooking it.

But

As long as they haven't previously been sitting out for an extended period of time, most likely you'll be ok for 1 1/2 hours since the steaks will be cold when set out. Make sure that they remain tightly wrapped/covered to minimize exposure to air.

I suppose, in the end, this is more a question of how you like your steak cooked. If you like it rare, then you probably won't want it out very long in the first place. If you like it well done, then really you can leave it out for hours and it's not going to make much difference.

For the elusive medium, you have to have the steak around room temperature, or the inside is going to cook too slowly. That'll leave you with the involuntary medium-well, or a band of "under done" meat.

So judge based on the ambient temperature, not arbitrarily by time. Sitting beside the grill for 5 minutes in the summer in the south will bring your steak up to an acceptable temperature. On the other hand, if your house is 50 degrees year round though, it can probably sit on the counter for a while without danger.

Two hours is pushing it. It should be ok, but I never recommend letting one sit for more than an hour. If you can lean towards 90 minutes, do that. Two hours is the absolute maximum.

The official time for food to be left out before it is considered unsafe to eat is 4 hours.

http://www.idph.state.il.us/about/fdd/fdd_fs_foodservice.htm

However like all government guidelines, this certainly takes into account a large margin of error. Your steaks will still be safe resting after an hour and a half outside the fridge. Personally I leave my thick steaks out for two hours to come to room temperature.

It is however preferable to salt your meat as far ahead of time if you can manage it.

http://www.seriouseats.com/2011/03/the-food-lab-more-tips-for-perfect-steaks.html

If I forget to get steaks out the freezer and am in a hurry, I microwave them in tightly sealed plastic for a minute on each side, and then broil/grill.

If the steaks are already at least thawed to fridge temperature, leave them out for a shorter time on the counter, or even put them in the oven at 150 before broiling/grilling.