Well, for a start, I think a generic VB syntax sheet would be useful. After all VBA is just a stripped down Visual Basic (more similar to VB6 than VB.NET, so no LINQ queries on your cells!) with the Office object model. I really like this C# to/from VB.NET sheet. And since people rarely use VBA to develop complex classes, once you're familiar with the basics (subs, variables, loops, branching) it's pretty much standard programming from then on.
As for the object model, if you're familiar with the .NET documentation, you'll find that the VBA/excel help is structured similarly (with lists of methods and properties for each object). Things usually start to go smoothly once you're familiar with the essential objects:
I've looked for a few visually structured documents, like this, this and that (caution: from old excel version), but they appear very mildly useful. There may be some gems out there, but problem-specific google searches usually works pretty well.