Is there an in-game list of my current items' effects?

Solution 1:

Sadly, no. There is no in-game list of what the items do. You can select Collection from the main menu to see a list of the items you've found thus far, but even that won't tell you what each item does.

The best source for item information I've found is the Binding of Isaac Wikia. It has a complete list of the items, as well as a description of what each item does.

Solution 2:

As @Tristan said, there is no in-game list of what the items you have collected do.

However, if the items you've collected have increased (or decreased) your stats, the top bar when you hit escape (just below the 'Paused!') provides details for said stats (speed, tears, damage, and range).

Remember each character starts with a different set of stats when looking at this view - see http://bindingofisaac.wikia.com/wiki/Playable_characters for details).