Here's a list of links and resources on XLIFF and localisation. Feel free to update this page 
Standards
XLIFF articles
Articles on XLIFF/TMX originally published at IBM developerWorks by Rodolfo M. Raya (Maxprograms): Part 1, Part 2,Part 3
XLIFF 1.1 whitepaper (From XLIFF TC documents)
SHEN Hua Pin, ZHU Ting Yong: Localisation with XLIFF (IBM).
Tim Foster (SUN): Using Translation Technology at SUN Microsystems
Peter Reynolds; Tony Jewtushenko: What Is XLIFF and Why Should I Use It?
Blogs/Wikis
Software
Translate Toolkit converts multiple formats to XLIFF or PO. Allows checking, greping and counting of XLIFF files.
Heartsome XLIFF/TMX/TBX editors (not open source)
KBabel PO Editor (limited support for XLIFF)
Pootle web-based translation portal (supports translation of XLIFF and PO files).
Rosetta web-based translation portal. (not open source)
Irma web-based translation portal. (not open source)
Transolution GTK/Python based XLIFF editor with Translation Memory support
Open Language Tools XLIFF editor and filters open sourced by SUN Microsystems
Swordfish XLIFF editor written in Java with support for many different document formats. Published by Maxprograms.
LocFactory XLIFF editor for Mac OSX (commercial, free LITE version)
File2XLIFF4j Open source project that intends to produce converters for HTML, Excel, and Word documents.