Also, check out the upcoming book 'The Obstacle is the Way' by Ryan Holiday - http://www.amazon.com/The-Obstacle-Is-Way-Timeless/dp/159184...
However, he does a good job of giving a basic introduction and framing for Stoic concepts. I think it's easier to digest the Romans (particularly the concise and acerbic style of Epictetus) if you are somewhat familiar with the subject. I got much, much more from Epictetus than I did from Irvine, but he is, I think, a valuable on-ramp.
I'm also not sure what the big deal is with Marcus Aurelius. Compared with The Enchiridion and even Seneca's letters, it's haphazard and dull. I'll give it another shot once I'm done with all of Seneca's letters.
Personally, I would start with Irvine, then the George Long translation of The Enchiridion (it's more poetic than the Carter translation, IMO). I'm about half way through Seneca's Letters, and while enjoyable, he takes a long time to cover the same insights as Epictetus.
(aside: on my 3rd or 4th reading of The Enchiridion, I wrote brief notes on each part, which you can find at http://thiscodinglife.com/dissecting-epictetus/intro)
I had the same initial reaction with Marcus, but honestly it might be because I didn't have the right translation (pick Gregory Hays's!!) and not enough background on the man. I would highly recommend watching this short series that mentions both Epictetus and Marcus: https://www.youtube.com/watch?v=nLD09Qa3kMk I truly think you'll see the Meditations in a different way after watching this. Also, Pierre Hadot has a very good (but scholarly) analysis on it in The Inner Citadel.
And for Epictetus, I always introduce him with the story of the Vietnam prisoner of war James Stockdale who in a way relied on stoic principles to endure the tortures he was inflicted. He wrote and lectured about the lessons there, Google him around.
I'm not a big fan of Guide to the Good Life either -- mostly because I think it takes a very profound (and by no means simple or obvious) set of ideas and reduces it to a kind of intellectual fad diet.
For something weightier, you might look at the works of Pierre Hadot (Philosophy as a Way of Life and What is Ancient Philosophy?), both of which contain excellent discussions of stoicism.