I've got a requirement for showing thumbnails of arbitrary websites. I need to be able to show small thumbnails (120px by 90px), and larger thumbnails of around 480px wide. I'll need to specify the queue and invalid placeholder images and preferably have a pingback when the queued images are processed so I can respond appropriately. I'd also need a simple API I can use either directly embedded in my HTML, or from a simple web request to queue the images.

I've been looking at various services ranging from low-fi services, to large scale ones - here's some examples:

www.bitpixels.com

Uses Google AppEngine, seems like a prototype or a toy. Free!

www.websnapr.com

Tried using this, made a free account and requested a thumbnail. Waited a few minutes and refreshed a couple of times, and ended up having the account banned. Free is tricky yes, but if I can't try it out successfully I'm disinclined to pay.

www.shrinktheweb.com

Free account seems to be very quick. Lots of documentation on the site, and even covers local caching of the images to your own server (documentation mostly in PHP). Quality of thumbnails look good, and there appear to be sufficient options for setting thumbnail placeholder images and parameters for altering how the thumbnailing is done. Also supports large 'screenshots' of URLs - very useful for me. Discovered the PRO pricing is an à la carte menu, allowing me to select just the features I want and keep the monthly cost low. Excellent stuff, have decided to use this service.

www.thumbalizr.com

Good coverage of thumbnail sizes and control options - even allowing specification for browser width when thumbnailing. No ping-back, but I can live without that. Supports local caching of images with PHP API, would prefer .NET, but can port it if necessary. Looks like a fairly professional service but seems fairly expensive for the number of thumbnails you get to generate.

apologies for lack of proper linking - spam protection!

I'm not entirely convinced by any of them, and since this will be a long term service I'd like some stability and support. I'm willing to pay for the service, but I'd want something that fulfills most if not all of my requirements for that.

I should also mention that we're hosted on Windows under IIS, so local solutions involving Xvfb and the like sadly can't be used for this project.

So my question is: what services do you use? How have they panned out, are you happy with them?