Most of you requirements except the need for SDB and S3 are well satisfied by Rackspace. Rackspace is also coming up with a new feature, similar to S3 called cl

Most of you requirements except the need for SDB and S3 are well satisfied by Rackspace. Rackspace is also coming up with a new feature, similar to S3 called cloud files. But no equivalent for SDB. Since you are in development Rackspace's low end boxes (like 256M with 512 bursts, etc.)charged nominally for bandwidth will do fine. Whereas Amazon has got fixed boxes with 2G or something as far as I remember, I took it like 5 months ago. For a dev box where there is no/not-much user traffic, a low end shared box from Rackspace if a good option. Its highly efficient on the budget. Once you have used it for dev phase you will have more knowledge and confidence on what Rackspace can do and what not. So you can decide whether to use it for prod or move over to something else. Rackspace has got a monthly billing and anytime cancelling option. It works fine on budget as well as it gives you control over things if they are going beyond what you initially thought, as you can see the usage in real time (may be a few hours late at max). They had a money back policy too, about 4 months ago when I signed up, for the first month if the user is not satisfied. About problems: EC2: very less problems. But remember these are commodity hardware, measly boxes, the moment you start too many process (if doing any mutli processing) the box's response time mounts exponentially :-). Multi-threaded is fine. S3 - have been using for storing images and haven't had a problem so far. You have options to save your EC2 image to your S3 space regularly to keep backup server images. That costs you in terms of the space required on S3. SDB: I hope you are aware but will still iterate that this is a key-value datastore, not relational. I will say it is very much in the works. It does a lot good at most of the times, but lack of a group-by, only text data, only lexicographic sort (which forces the user to put even numerical data in special formats to sort on it), a bit ill defined mutli-valued attributes, number of attributes allowed to put at each request and overall number of attributes for a item are a few bumps in the road. But once you read the docs and be regular with the AWS forums most of these get solved. Rackspace cloud server: Only problem I have faced SSH is slow sometimes. Rackspace cloudfiles: haven't used. But I know that you can automate your cloud server backup to cloud files, that costs. Again, as you mentioned LimeLight, that's another factor, that makes Rackspace more suitable for you. So I guess you best bet is to start off with Rackspace for now and see how it goes. Hope that answer helps.