Here's a photo of the tool I've been mentioning
(and a close up further down)
It' called Scor-Pal and is made exclusively for scoring cardstock and paper. It is a fairly rigid plastic, about 12" x 14", and about 1/2" high, with a recessed area for placing the paper, and then lines recessed further in for scoring. There is a ruler on the top and both sides, and it will handle up to 12 x 12 sheets, with score lines every inch and additional ones. It comes with it's own scoring tool which snaps into place at the top as shown so it won't be misplaced, although I think another bone folder could substitute.
There is a fabulous website at Scor-Pal that actually has online magazine articles with step by step photos of projects using this tool.
I found it to be very user friendly and accurate. It takes an initial practice run to decide how hard you should press depending on the paper thickness used but that's it! I found it so simple to make diagonal lines, and for fans of faux-grid, it's a snap! No more measuring for so many styles as all the work is already done (and you know how I love special folds). There's a line at 4 1/4" for scoring A2 cards in half and many more at various intervals.
The packaging comes with some ideas and as you can see from the website there'll be no shortage of ideas for future use.
I picked mine up at a local Archiver's (I have to admit I went in with a 30% off coupon planning to buy a Scor-It! when I noticed this and knew instantly it would work better for my needs) I think this will be a product I'll actually use every time I make cards.