Highly Recommended Links:

NASA Earth Observatory
An excellent site from NASA with articles, satellite images and much more. A valuable resource for keeping up to date with ongoing research into issues associated with glaciers and global change, as well as an excellent reference site. Worth exploring in detail. There is an opportunity to sign up for a free weekly update telling you about the latest stories, data, and other points of interest that have been added to the site. An excellent resource for University students, interfacing directly with original scientific research.

National Snow and Ice Data Center (NSIDC)
A huge repository of information conveniently organised into different sections that will be of use to professional researchers, students or teachers. Includes, amongst much else, the following: 

"The Cryosphere", including "All about Glaciers" (part of the NSIDC site)
Produced by the National Snow and Ice Data Center (NSIDC) this site has extensive sections on glaciers, snow, etc., each with photo galleries, Q+A sections, links, glossaries, etc. Especially useful for non-experts, the site is pitched at level that should make it user-friendly for beginners, as well as containing some more sophisticated material and links for more advanced users.
Snow and Land Ice Data (part of the NSIDC site)
A huge range of data sets from the NSIDC covering everything from huge photo-libraries to raw ice-core data. A treasure trove for the researcher or student
Greenland Summit Ice Cores Data (part of the NSIDC site)
Everything you could want from the GRIP and GISP2 projects including summaries of the projects, final reports, bibliography of work emerging from the projects, and even the raw data for download. An example of the level of depth you can get if you start burrowing into the NSIDC site!
Ice Core Gateway and World Data Center for Paleoclimatology
Searchable site with access to information about, and data from, ice cores from around the world.

Global Land Ice Measuring from Space (GLIMS)
A GLIMS article from the NASA Earth Observatory site

"Glaciers online"
Based on Hambrey and Alean's  book "Glaciers" (Cambridge University Press, 2004), this site contains almost all the photos, at fairly high resolution, and corresponding captions. The material covers glaciers and glaciated terrain from all over the world, and may be useful in teaching glaciology and related subjects. 

A selection of other useful and interesting sites:

"Glacier" Educational web site
(Periodically off line) A co-operative effort between researchers and educators to provide a web site  for the general public and  a hands-on, inquiry based, thematic curriculum for middle school. User friendly and accessible to the non-expert, and conveniently divided into sections such as "Ice and Landscape", "Ice movement" and "Meet a Geologist" this is another good site for teachers, school students, and non-experts.
"About Antarctica" from the British Antarctic Survey.
Part of the BAS site, this section provides well informed, detailed and sensible answers to common questions about Antarctica such as "When did the ice sheet form?" and "Is the ice sheet melting because of global warming?". There are also details of BAS scientific projects such as Global Interactions of the Antarctic Ice Sheets.
Satellite Image Atlas of Glaciers of the World
USGS site with direct links to the so-far-published sections of this valuable resource, with data about glacier extent, sea-level impacts of glacier change and, of course, some satellite images.
Geomorphology from Space
A gallery of space imagery, each section treating a geographic region where a particular landform theme is exemplified.  Commentary, photographs, locator maps, and sometimes a geologic map accompany each plate. Includes a "Glaciers" section. The thumbnails don't just lead to bigger photo's but to extended pages with maps photos and other info. Designed for use by the remote sensing science and educational communities to study landforms and landscapes.
Physical Geography Web Resources
A link jump site to lots of other sites categorised by physical geography topic, including a set for glaciers and glacial landscapes.
The Virtual Geomorphology
A broad range of articles, on-line text books and discussions about geomorphology by a broad range of contributors. There is a lot of material in here. 
Tom Lowell's Glacier Image Database
Photographs of glaciers and glaciated landscapes categorized for ease of use by students and teachers.
Danish Polar Centre  and What's on in Greenland
Useful for information about Greenland: Scientific from the DPC and tourist/general from "What's on"
International Glaciological Society and IGS (British Branch)
Links to the society's pages. Now includes full contents lists for of the Journal of Glaciology, but no actual access to the papers, sadly.
BBC news: Kazakhstan glaciers melting and NGrip ice core and Thinning Arctic sea ice
BBC news provides non-specialist summaries of many tpical aspects of glacier behaviour and environemntal change. Searchable site, turns up some interesting items at the "popular science" level.
Glaciers Online (Portland State University)
Information, photos, maps etc relating to glaciers of the western USA.
All about glaciers
A little page with some useful links.
World Atlas of Panoramic Aerial Images
Not specifically glacial, but a great geo-resource.
an on-line discussion group
on-line discussion and news

This is only a tiny sample of the glacier related web sites that are out there, but it's easy enough to find more through search engines or through links from the sites listed above. When you look at these sites, make sure you know what level they are pitched at. If you are working on your undergraduate dissertation, you should beware of the simplified information that you might find on a popular or junior-school web site, and if you are trying to find out just the bare basics about glaciers you don't want to start with the raw data from Siple Dome!