I have about 450 stock photos on my hard drive, which are all numbered, but they weren't uploaded on all sites, and some of them are skipped at some sites.
For example:
on Shutterstock, i uploaded all from 0-450
On Istock:  0-100, then 220-315
Fotolia: 0-15, then 100-130
and so on...

I'm already loosing track of what I uploaded and where, so I'm looking for an idea how to keep everything tracked so I know what I'm doing.
Do any of you have any advice? Like writing it in Excel or something like that...
Thank you in advance!

here's my solution, using excel

http://cascoly.com/mssub1.asp

An excel sheet or database works fine for keeping track of what is accepted where.
For everyday uploading routine I create a separate folder per agency where I copy all images to upload once they are processed and keyworded. That creates multiple copies per image, but only temporarily.
Once uploaded they go in a respective sub-folder "up", and from there they are deleted when accepted/rejected.
This makes it easy to see what was not uploaded to a specific agency with one look.

I have roughly 1100 images now and I sort them by folders. It goes something like this

Top level:
Approved
Pending Approval
Submissions
WIP (Work in Progress)

2nd Level:
Illustrations
Vectors
Photos
Etc.

3rd Level:
Technology
Landscapes
Healthcare
Food
Etc.

I add more sub folders and sort them if things start to get out of control.

I use a Mac and I find the tag system to be really useful. I use color tags on folders and files to indicate which websites I've submitted to where it was approved. Take for instance, I use Red for SS and Green for FT. I submit to less than 10 agencies, so this system works well for me.