I'm a big advocate of Google Docs, and, well, pretty much all things Google - I've decided to set up some spreadsheets to make my planning a little easier. The layout is simple, I can access them easily from my email and it's free!
First thing is a budget spreadsheet with a total sum formula so I can easily see what's pushing things over-budget and I can easily break things down into subcategories from there.
Second thing is a guest broken down into family, friends, etc., with a count formula so every time i add a name I can see the updated total guest count.
I assume most people are pretty computer literate but if anyone wants some help setting up spreadsheets like this, just let me know and I'll be happy to do so!