Writers with iPhone should check out Write Chain, an app which provides motivation by storing word counts for each writing session and tracks the total words written across all sessions.
The "chain" part of the whole strategy is to try to write for as many days in the row as possible. If you miss a day, you break the chain...unless you change the settings to allow yourself some leeway.
Cost of the app: FREE, at least right now. Check out the rest of the How Now Not To Write site for helpful tips for writers from Jamie Grove.
Found out more about this app at the Write Chain site.
Related: List of other iPhone apps for writers.