Photobucket for a 600 px wide photos, and webshots for thumbnails.
Heard good things about Imageshack.
Resizing anyway will be necessary.
In freeware IrfanView (I know only this one) it's easy:
- open file, menu: View/Display options/Fit only big to screen,
- press left button and drag by mouse to select the significant part of the photo, menu: Edit/Crop selection,
- menu: Image/Resize/ Best fit to desktop (or whatever you like), press OK,
- menu: File/Save as (.jpg, 75-80% quality).
Done. Ready to upload.
Optional, before save as: Image/ Auto adjust colors, then Image /Effects/Effect browser/ sharpen at 10% (or unsharp mask). Then save as.
All is visible and straight forward, unlike the Photoshop (for me

).
HTH