Great topic, and it's one that I have gone back and forth on!
I am Synergist in the sense that God works with us in salvation. I am a Monergist in the sense that "For in Him we live and move and exist, as even some of your own poets have said, ‘For we are also His offspring.’" (Acts 17:28 HCSB). Our universe derives from God. Our very being, of course, derives from God, so in that sense I agree with Aspen that God sets the stage. However, I very clearly believe God himself chooses to allow things to happen, even with the divine foreknowledge necessary to know our hearts (and therefore actions) intimately.
In addition to this, the two ancient strands of Christianity (Eastern Orthodoxy and Roman Catholicism) are Synergist. I view the advent of St. Augustine and later Calvin(ists) and Reformed as not so much error, but just a varying perspective on salvation. (Two sides of the same coin, if you will.) I think Reformed theology is valuable, but I also think that there can be an unhealthy emphasis on this theology and topic at times.
If you read men like John Wesley, a notable Arminian, his language doesn't sound that distinct from Calvin in terms of the sovereignty of God. I'll be happy to provide a sermon where he discusses the issue and makes some orthodox and Biblical statements. Arminianism is not Pelagianism or Semi-Pelagianism as some would want it to be.
With that said, the biggest thing for me is the ordo salutis (order of salvation). Monergists see regeneration taking place at least simultaneously or just before faith. In general, it works like this (with perhaps some variation):
Predestination => Election => Calling => Regeneration => Faith => Repentance => Justification
The Arminian (Synergist) path varies, with the key being Prevenient Grace:
Foreknowledge => Predestination => Election => Prevenient Grace => External Calling => Repentance => Faith => Justification
*Sometimes you'll see Repentance & Faith lumped together.
I've seen many a Calvinist speak to the notion that foreknowledge is just God knowing beforehand what you will do. I would take foreknowledge to the level that God knows us intimately, meaning he does know what we will do not because he looks down the corridors of time, but because he knows our hearts so well that he knows what we will do. It's very difficult for us to wrap our heads around God knowing the same knowledge at the time of our first creation (thought even) as he does at our earthly death.
Prevenient Grace and Regeneration serve a similar purpose, even though some will vehemently deny this. In the Wesleyan thought, Predestination and Election are more corporate, and Prevenient Grace is just a more general working of God paving the way for us to have faith.
I do what to emphasize that these illustrations can be atemporal. I think we tend to think very linearly and so that makes us think that if something is addressed after, it will happen after in time. Some of these steps may overlap or take place at the same time, for both the Synergist and Monergist.
All of the above said, I very much want to emphasize that the western notion of one and done saved is false. It's a lifetime of being saved (Paul uses this tense in at least one spot to my knowledge), and Ieft out sanctification in the above illustrations just to focus on the first part of ordo salutis.
