Hosting/Scaling- We Plan To Get Digged/stumbled

Our website/app is on a shared host (downtownhost.com - who are great btw - I strongly recommend them).

Now have a question for the experts here:

We have come up with a plan to give away some freebies to our visitors and we feel there is a very good chance that we will be digg 'ed/Stumble 'd.

I need suggestions from experts as to how to go about this from a hosting perspective.

1. Go for Amazon or Gogrid.com?
2. Go for mediatemple.com or mosso.com? Not sure with all the reviews posted here.

I don't want to go for a full blown clustered hosting - with high fixed costs - we won't mind paying based on how successful or not our 'freebie' exercise works.

A little bit about our site - it's an ecommerce site running on LAMP and uses imagemagick. Users upload images to our site and
tell us what they want with an annotation tool in a UI. We give em a price and they can pay us. They pick up the edited image back on our site when it's ready

- Sorry bout not being able to give you any 'technical' details about CPU usage etc., - I am more of a layman! But as I said a shared account at downtownhost.com seems to be holding up. Our current traffic averages about 100-200 visitors a day - with an average of about 50 images uploaded everyday.

- Think that the above description should give a fair idea of computing/resource requirements.