Books:

MPLS - Implementating the technology by Eric W. Gray (Addison-Wesley)
MPLS: Technology and applications by Bruce Davie and Yakov Rekhter (Morgan Kaufman)

Introductory Articles:

MPLS Architecture - Cisco at RIPE
Introduction to MPLS - Nortel presentation
Selection of signaling protocols for MPLS - Data conenction white paper
Introduction to MPLS services - Cisco presentation
Introduction to MPLS - Trillium white paper
MPLS architecture - RFC 3031
Summary of MPLS related MIBs
MPLS Architecture - Cisco Press chapter

Advanced topics:

TE:

MPLS TE requirements - RFC 2702
MPLS TE - Nortel presentation
MPLS TE - Juniper presentation
MPLS TE - Juniper white paper
MPLS TE - Avici White paper
MPLS TE Initiatives comaprison - Netplane white paper
MPLS TE - Global Crossing paper

Detailed TE page ....

Layer 2 VPNs:

Layer 2 VPN architecture - Cisco presentation
PPVPN - Kireeti's presentation
VLL using MPLS - Foundry white paper, presentation
Layer 3 versus Layer 2 MPLS VPNs - Foundry white paper
Layer 3 versus Layer 2 MPLS VPNs - Riverstone white paper
Interoperability report on L2 MPLS VPNs - Foundry

Related IETF drafts

Transport of Layer 2 Frames Over MPLS 
Encapsulation Methods for Transport of Layer 2 Frames Over IP and MPLS Networks 
Encapsulation Methods for Transport of Ethernet Frames Over IP and MPLS Networks 
Encapsulation Methods for Transport of PPP/HDLC Frames Over IP and MPLS Networks 
Frame Relay Encapsulation over Pseudo-Wires 
Encapsulation Methods for Transport of ATM Cells/Frame Over IP and MPLS Networks 
 

QoS:

MPLS support for differentiated services, RFC 3270
QoS - Avici white paper

Protection and restoration:

MPLS P&R - Data connection white paper
MPLS recovery framework document - IETF Draft

VPNs:

Introduction to VPN - Nortel presentation
What is a VPN - Paul Ferguson (Cisco)
What is VPN - Juha's presentation
MPLS VPNs - Cisco Presentation
BGP VPNs - Juniper white paper
BGP VPNs Applications, Juniper white paper
MPLS VPNs - Data connection white paper
BGP VPNs - RFC 2547
A core IP MPLS VPN architecture - RFC 2917
Scalable VPNs - IEEE Comm Paper (Alcatel)
MPLS VPNs - Cisco press chapter

Security in MPLS:

MPLS security - Cisco white paper
MPLS VPN security - Mericom white paper

GMPLS:

GMPLS Introduction - Cisco at RIPE
Introduction to GMPLS - IEEE Comm paper
GMPLS Related drafts

Signaling 

Resource Reservation Protocol 
RSVP, RSVP-TE, RSVP-TE for GMPLS
LDP, CR-LDP, CR-LDP for GMPLS
Using CR LDP for TE and QoS - Nortel *

Routing

OSPF, OSPF-TE, OSPF for GMPLS
ISIS, ISIS-TE, ISIS for GMPLS

Related topics

Resolving route in MPLS, Juniper white paper
RSVP For TE, Juniper white paper
Optimizing routing - Juniper white paper

Standards:

IETF MPLS working group (mpls)
IETF GMPLS working group (ccamp)
Traffic Engineering working group (tewg)
Resource Reservation Protocol (rsvp)
OSPF
ISIS
PPVPN (PPVPN), PPVPN related drafts
Psuedo wire (PWE)

MPLS Repositories

Multi layer routing page
MPLS Resource center
MPLS Forum
Vinay Ravuri's page
University of New Hampshire Inter operability lab
Advanced Internet Lab - GMU