I found this great tutorial full of wonderful tips for making realistic shadows on your scrapbook layouts with Photoshop... Also by Megan Turnidge with a set of layer styles included. 
eta: realistic cluster shadows tutorial (12/11/12)
I found this video tutorial for realistic shadowing of clusters on Kristin Cronin-Barrow's blog, done by Christy Haig here.
eta: 5 more realistic shadows tutorials (12/13/12)
Here is the Sweet Shoppe link to several more awesome shadowing tutorials including: Basic Shadowing Techniques: Layer Styles, Basic Shadowing Techniques: Anatomy of a Page, Shadowing Acrylic and Plastic, Lighten up, baby!, and Using the Distort>Wave Feature on Shadows in Photoshop [enJoy!]
Thanks Shawna, I already had that one on the list here, but I may not have actually posted about it.
It IS a brilliant tutorial - I was just looking at it the other day (must've found the link via the list Marisa mentioned?), there are so many little details I wouldn't have thought of! And it's funny, because if I were physically drawing the elements, I'd "know" to do things like bend the shadow to be more on the item directly below than the background...but I forget that when shadowing in Photoshop.
Those styles are super-helpful too, I wouldn't even have a clue how to handle a transparent element!
Oppps -- I only checked the post titles but not inside the tutorial sticky post its self.
I liked Megan's discussion of shadows & such... However, does anyone know if these styles would work in PSP?
I know this is the Photoshop forum, and maybe I shouldn't venture over here, but I'm so desperate to learn more stuff about digiscrapping (and how to do things better, easier & more efficiently) so I come to look at the tutorials & see if any would work for me - I really want to learn different things about digiscrapping (hope you don't mind).
Thanks for sharing! That has definitely helped me look at my layouts differently *sigh* I must practice more! Her stuff is amazing.
@Lizanne, This is on Megan's blog:
So, give it a try! I always use Megan Turnidge's shadows on my layouts and apply almost every option she explains in her tutorial. I love shadowing! It can make a digi layout look like a paper one sometimes...
I don't have Photoshop Elements.... my program is PSP (Paint Shop Pro).
Sorry to get your hopes up, Lizanne... next time I'll pay attention to that one letter (PSE/PSP)
I have no idea how to shadow in PSP, so I can't help you there... sorry.
Thanks for sharing!!
Wow! I didn't know Meghan was still sharing these for free. And she updated her post with images and tips! I've been using her shadows for years (and I'm usually so busy that I don't have extra time to tweak them, and still I get comments about the great shadowing I do, and every single time I think: I owe it all to Meghan T.
How fun that you guys here have found them as well!
Thanks ladies, I will check it out.
Thank you I am going to check it out.
Wow! A lot of information to digest. Thanks for the links.
Thank you. This will be very helpful. I like the tutorial on lightening the shadows on light papers a lot.
Thanks so much!