Here are some links to various helpful websites, downloads, etc.    (Main Page)

General Linguistics
Linguistic Association of America (LSA)
Linguistic Association of Great Britain (LAGB)
Deutsche Gesellschaft für Sprachwissenschaft (DGfS)
The Linguist List
Also, some of the Max Planck Institutes have programmes in LinguisticsLinguistics Fieldwork 2004

Typology
Association for Linguistic Typology
Typological Database System Project (I find this page difficult to view with Safari, easier with Firefox)
Autotyp
Surrey Morphology Group (Typology Projects)
NegTyp
StressTyp
Eurotyp
The Ethnologue (edition 14)
Universals Archive

Sino-Tibetan/South Asia/Southeast Asia
Himalayan Linguistics (a refereed, online journal)
Digital Himalaya
The School of Oriental and African Studies (SOAS)
Bibliography for (understudied) South Asian Languages (maintained by John Peterson)
Himalayan Languages Project
Linguistics of the Tibeto Burman Area (LTBA)
Journal of South Asian Linguistics (JSAL) (a refereed, online journal)
Centre for Nepal and Asian Studies, Tribhuvan University (CNAS)

Language Documentation (selected sites and projects)
(many of these sites merge with the Endangerment & Downloads sites too, so see below)
Dokumentation Bedrohter Sprachen (DoBeS)
The LACITO Archive (CNRS, Paris)
The Chintang & Puma Language Documentation Project (CPDP) (funded by DoBes)
Linguistics Fieldwork 2004
ELDP at HRELP
Documentation projects & initiatives at UC Berkeley
Survey of California and Other Indian Languages at UC Berkeley
Puma & Chintang/CPDP (Nepal)
Yurok Language Project (UC Berkeley)
Saami (Pite in Sweden and Kola in Russia)


Language Endangerment/ Maintenance/Revitalization/Revival/Promotion
(See above too)
Hans Rausing Endangered Languages Project (HRELP)
Endangered Languages Academic Programme ELAP (and ELDP for documentation, in particular) at SOAS
UNESCO Red Book of Language Endangerment (note also the Green Book on language revitalization, ERIC citation here)
Living Tongues Institute for Endangered Languages
Foundation for Endangered Languages
Terralingua
Alaska Native Languages Center

Software (and other useful stuff) Downloads
The R Project for Statistical Computing (statistics software)
Praat
SIL Unicode Fonts
Audacity (good for quick-n-free digitization)
Toolbox (Data analysis & management tool for field linguists)
VassarStats (not a download, but an extremely useful & easy-to-understand resource for statistical computation)
Virtual Box (like Virtual PC for Windows emulation, but free)