Difference between WCS, WMS and WFS

(Writing this entry hoping it makes clear of a novice GIS developer like me)

First the terminology...
WMS - Web Map Service
This service only serves image files, nothing else. You get pngs,gifs, jpgs or tiffs. You can also display coverage data but your actual data is mapped to imagery. For example, in geoserver, you can actually serve bathymetry (elevation including seas) data in geotiff to clients, but your coverage data including elevation is mapped to RGB data in png.

WCS - Web Covarage Service
From the introduction part from OGC 's WCS Implementation Standart Document.

The Web Coverage Service (WCS) supports electronic retrieval of geospatial data as "coverages" – that is, digital geospatial information representing space-varying phenomena.

A WCS provides access to potentially detailed and rich sets of geospatial information, in forms that are useful for client-side rendering, multi-valued coverages, and input into scientific models and other clients. The WCS may be compared to the OGC Web Map Service (WMS) and the Web Feature Service (WFS); like them it allows clients to choose portions of a server's information holdings based on spatial constraints and other criteria.

Unlike the WMS [OGC 06-042], which portrays spatial data to return static maps (rendered as pictures by the server), the Web Coverage Service provides available data together with their detailed descriptions; defines a rich syntax for requests against these data; and returns data with its original semantics (instead of pictures) which may be interpreted, extrapolated, etc. – and not just portrayed.

Unlike WFS [OGC 04-094], which returns discrete geospatial features, the Web Coverage Service returns coverages representing space-varying phenomena that relate a spatio-temporal domain to a (possibly multidimensional) range of properties.