Public read-only servers?

Are there public read-only servers (commercial or free) for non-marginal traffic (thousands or tens-of-thousands of requests per day)?

EDIT: Tile requests would be one need. Another would be doing searches on data (e.g. find me the intersection nearest to a point, give me the bounding box of a block containing an address, those sorts of interrogrative queries though I don't have too many specifics in mind). Mostly, I'm curious about what is available while I play around and build applications, since creating a server-side db based on the full planet file is cost-prohibitive.