I know it's not a WebApp (at least last time I checked), but I'd recommend you go with the same product almost every small company in the world uses - Quickbooks. Everything else is just a niche player. Quickbooks will take you all the way to just before 500 employees and going public (Speaking from experience. ) Your financial software should be something you don't even think about. Quickbooks captures that model -plus, every accountant/bookkeeper in the world knows how to use it.

If you are dead set on having a webapp, and are planning on growing, the elements that people are looking for, books that are SOX clean, online expense and Purchase Requests, can be found in products like Netsuite.

Our company went the QuickBooks->Netsuite->OracleFinancials route. And, no matter _how many times_ I go through that routine, OracleFinancials _always_ ends up being a pain to deploy - no matter how much we pay the consultants to make it "smooth, pain free."