It's become pretty much a custom to start spatial epidemiology or medical geography textbook / lecture with an example of John Snow's cholera investigation in 1854 Soho.
He's definitely still remembered in the current literature and even appeared on top answer to a recent question on this site.
Could you give some recent examples where mapping, GIS or spatial analysis provided significant contribution to understanding and explaining an epidemiological issue?
Stan Openshaw's GAM work finding a cancer cluster around an incinerator in Gateshead when everyone expected it to be on the other side of the country by the nuclear plant. You can read parts of the original paper at http://books.google.com/books?hl=en&lr=&id=qR0vfnwVuU0C&oi=fnd&pg=PA7&ots=0v2P9rhN8R&sig=tryyfcErunxpptshJ4cBagl6mDw#v=onepage&q&f=false
I nominate Ushahidi.
"The Ushahidi Platform allows anyone to gather distributed data via SMS, email or web and visualize it on a map or timeline. The goal is to create the simplest way of aggregating information from the public for use in crisis response."
I particularly like the H5N1 outbreaks time series when visualized in Google Earth. There is a KML and a blog page about it by the author, Declan Butler. To display you need a post 4.0 version of Google Earth, and it might be useful to slow down the Animation Speed in the Date and Time Options dialog.
Mapperz nominates Bjørn Sandvik
http://blog.thematicmapping.org/2008/06/proportional-symbols-in-three.html
Created the Thematic Mapping Engine (TME) and API which enables you to visualise global statistics on Google Earth.
Recommend for an introduction to the Subject "Using KML for Thematic Mapping"
I would nominate Martin Kulldorff, maker of the SatScan software that is one of the most popular disease clustering/surveillance tools used in epidemiology.
The Seattle Times tracking methadone's related deaths across socio-economic status of neighbourhoods.
(Source, methods, background)
Consider to take a look at this EU FP6 project: http://www.eden-fp6project.net/ - EDEN (Emerging Diseases in a changing European eNvironment). The publications which resulted from this big project are available here (as map) and here (as list).
I don't know if it counts as "epidemiological", but Dr Clyde Hertzman at the University of British Columbia is a well known user of GIS in the field of childhood health and early childhood development.
http://www.earlylearning.ubc.ca/maps-and-data/
Dr Hertzman won the Canadian Health Researcher of the Year Award 2010, so he must be doing something right!
This is a different answer to the question of "a modern day Snow" -- How might Snow have used modern day visualization tools to make his case better for the Broad Street pump as the source of the epidemic?
The HistData package for R (https://r-forge.r-project.org/R/?group_id=574) includes all the data files (streets, deaths, pumps) from John Snow's map, and now includes a function, SnowMap() to draw a variety of enhanced versions including Voronoi polygons for the pumps and 2D density estimates for the deaths.
install.packages("HistData", repos="http://R-Forge.R-project.org")
If the context for the question involved some hands-on component for students in a spatial/medical/cartography course, there is plenty here for activities or projects.
Just stumbled upon interesting marriage of technology and health research:
Wireless sensors and flu tracking.
Although mapping is not intrinsic part of the project, it definitely places high importance on spatial relations between individuals.