Here some pictures I selected for my next try to apply for iStockphoto - many thanks for your critique

The single pictures:
http://dl.dropbox.com/u/9134818/_MG_2590-Bearbeitet.jpg [nofollow]
http://dl.dropbox.com/u/9134818/_MG_4610-Bearbeitet.jpg [nofollow]
http://dl.dropbox.com/u/9134818/Studio-Fotosession-090-33.jpg [nofollow]

The gallery:
http://www.dropbox.com/gallery/9134818/1/iPhotoStock?h=f76460 [nofollow]

I wouldn't be optimistic. They appear to be way over-processed, unoriginal in their subject matter and not stock oriented. You need to understand a lot more about STOCK PHOTOGRAPHY or you will just be wasting your time.

Buy Douglas Freer's book and/or wait for Rob Sylvan's which will be available from Amazon UK on 17/8. I imagine the latter will be well worth the money from a guy who has been at the heart of microstock for 8 years now;

http://www.amazon.co.uk/Taking-Stock-Microstock-Creating-Photos/dp/0321713079/ref=sr_1_3?ie=UTF8&s=books&qid=1281041893&sr=8-3

The first 2 are so-so. Not exactly stocky.  I'm going to say poor lighting and and poor isolation on the third (because of the poor lighting, the isolation suffers). You'd be better off with a pic of a well lit well dressed cheeseburger.

Thank you for your feedback so far.

I reworked the pumpkin photo - now it should have really white background, but I agreed that it is not original.

I am wondering if the new landscape I attached to this post was more suitable. It is no HDR but I combined serveral layers for the photo. On one hand side, I am aware of the "over-processed" problem, on the other hand side, the top selling landscape pictures at Fotolia look also quite processed:

http://us.fotolia.com/id/12348626 [nofollow]
http://us.fotolia.com/id/3256956 [nofollow]

By the way, there are also German Stock photography books (for the German speaking guys) - I read this one:
http://www.amazon.de/Stockfotografie-ProfiFoto-verdienen-eigenen-Fotos/dp/3826658868/ref=sr_1_1?ie=UTF8&s=books&qid=1281124529&sr=8-1 [nofollow]

Basically it says that people photos sell best, but I would like try w/o people shots.

Reworked pumpkin shot:
http://dl.dropbox.com/u/9134818/Studio-Fotosession-090-33-1.jpg [nofollow]

Another landscape:
http://dl.dropbox.com/u/9134818/_MG_9972.jpg [nofollow]

Gallery:
http://www.dropbox.com/gallery/9134818/1/iPhotoStock2?h=934f16 [nofollow]

Your landscape is beautiful. But I wouldn't risk sending it for the application. I'll tell you why.
Yellow flowers is too yellow and blown out. IS doesn't like too saturated colors.

About overfiltering: As I understand, Istock says that image is overfiltered if processing affects print quality of the image.

The pumpkin is interesting but the front looks a bit dark. Also, I would clean up the flaws on the gourd with the healing brush and clone tool to make it look perfect.

The landscape is attractive but the focus looks soft. There is also purple fringing on the trees along the horizon.

I open my raw files in Lightroom, do there the basic work and then open it (via Lightroom) in Photoshop.

Actually Camera Raw 6 has this lens correction feature which should remove chromatic aberration, but obviously, I did not take care enough of it by myself for the landscape pictures.

I could imagine that your Nikon raw converter has a lens correction feature which removes chromatic aberration and (if you use older version of Camera Raw) Photoshop not.