"Al's Mix" from the container forum is very popular (you can also find more info if you search):

5 parts pine bark fines (fir is also OK)
1 part perlite
1 part spaghum peat

The roots will be able to breathe all season long. I'm in the process of re-potting all my plants to this mix but in the past few weeks I've seen an incredible difference.

Do some searching through the archives on the Container Gardening forum. You are sure to turn up a number of excellent different "recipes" for potting soil, all of which can be relied upon to provide good drainage and proper aeration and avoid compaction. In particular, look for anything recommended by tapla (Al), who is a regular participant and a recognized authority on container culture and potting soils. I've linked with one below, but there are numerous posts that will provide additional info.

There is a limit to how well potting soil will hold up over time. Even the best mixes will begin to compress and breakdown to some degree over an extended period, like multiple growing seasons. Not to mention that root growth in more permanent container plantings needs to be addressed by either pruning or potting up - as the roots expand, the soil diminishes. But any decent potting soil should last at least a full growing season

Here is a link that might be useful: Al's soil mix(es)