A few weeks ago, I noticed while taking a shower that the toilet was making a loud bubbling noise... soon after the noise started - the water in the shower began to stop draining. Since the shower and toilet are right next to one another, I assumed that there must be a clog in the drain somewhere down the line.
When I returned home from work that afternoon - the toilet flushed fine a few times before backing up again. It never overflowed - just backed up for a while before eventually subsiding.
We initially tried plunging and chemicals before resorting to calling a plumber to "snake" the line. When he showed up, he said that he needed to remove the toilet and snake from that drain because our house is built on a slab with no crawlspace, etc... he ran the snake out to the city sewer with a tip that looked like a spade, and thought that was enough to break up the clog. Before he left, he decided to run the snake back through with a different tip that was supposed to cut through any roots that may have invaded the line. He was unable to get that tip to work its way very far into the pipe, but said it was probably having trouble getting around a bend in the pipe.
I have had a few people ask about the vent, and if it was possibly clogged... could that truly be the problem here? The vent runs through the roof towards the back of the house - which is surrounded by trees - so being clogged with leaves and debris is not a long shot...
If I do look into the pipe and see a clog, what is the easiest/most cost efficient procedure for cleaning it out?
Thanks for your help!

Doesn't sound like a vent problem to me - sounds more like a partial blockage (and if you still have the problem, the plumber's snake probably only punched out the clog out some more, without actually getting rid of it). Here are the clues that lead me to this conclusion:

1) You got to understand toilet language: bubbles = clog, gurgle = venting problem. You said your toilet bubbles, not gurgles.
2) The water eventually drains on its own: that's a sign of water slowly seeping past a clog.
3) If it were a clogged vent, you're far more likely to see the water draining out of fixture traps due to siphoning than you are to see drains backing up.

Although considering that your clog has resisted "chemical warfare" and a snake, I can't help wondering if it's a) a broken or misaligned pipe, or b) a REALLY hard clog - maybe a child (or an adult with the brains of a child) flushed something metal or plastic, which will not be defeated with chemicals? Ask around your household if anyone flushed anything other than toilet paper and doo-doo recently.

Let us know what happens.
Moishe