Here is a list of some useful online TI-84 Plus C Silver Edition information and resources in English below, as of April 8th 2013:

First of all, the calculator features the following hardware:
-15 MHz Z80 processor (downclockable to 6 MHz)
-21.7 KB of user RAM (128 KB total)
-3.5 MB of user archive (4 MB total)
-320x240 & 160x240 resolution (the latter can be toggled with ASM)
-Horizontal scrolling support (z-adress)
-18 bit display for 262144 colors, where the TI-OS uses 16-bit mode with 65536 colors (15 in TI-BASIC plus transparency)
-Pictures can be either 4 bits 265x165 or 16 bits 133x83 and takes close to 22 KB of archive
-I/O and USB port
-Rechargeable battery
-Some TI-83 Plus and TI-84 Plus compatibility with TI-BASIC programs. ASM ones can be easily ported in some cases.
-On-calc TI-BASIC command syntax help (CtgHelp)

To create 4 bit color images (265x165, useable to store data for use with Pxl-test)
NOTE: TI-Connect can open 8ci pictures, but not create them. SourceCoder does the opposite: It can create them, but not open them. So to create 4 bit images, you must import a 265x165 JPG/GIF/PNG in SourceCoder, save it as 8xi then change the extention to 8ci. To view the result, open the 8ci file with TI-ScreenCapture (TI-Connect 4.0).

Official info/documentation
-TI-84 Plus C Silver Edition guidebook and getting started guides
-Official TI-84+CSE page

Connectivity softwares
-Windows: TiLP (limited CSE compatibility), TI-Connect 4.0 (lacks pic/8ci exporting support.)
-Linux: TiLP (limited CSE compatibility)
-Mac: TI-Connect 4.0 (lacks pic/8ci exporting support), TiLP (limited CSE compatibility)

Emulation
-Emulators: jsTIfied (cross-platform), TilEm2 (experimental 84+CSE support)
-ROM Dumpers: TITools ROM dumper (requires TiLP 1.17)
-ROM->.8xu tools: ROMto8XU

Programming documentation
-Z80 assembly: WikiTI
-TI-BASIC: New color commands and arguments, Official guidebook, TI-Basic Developer (doesn't include color commands/arguments)

Programming editors/compilers
-Z80 assembly:
-TI-BASIC: SourceCoder (Can export 8ci images, but not import them), TokenIDE (lacks CSE image support)

Where to upload your TI-84 Plus C Silver Edition games and programs:
-Omnimaga upload form (Max 1 MB)
-Cemetech upload form (Max 2 MB)
-Ticalc upload form
-TI-Planet upload form

Where to get, provide or ask help on Omnimaga:
-Programming and support forums
-Tutorials
-Tutorial upload form (takes 12-36 months for approval, or a few hours if you PM admin immediately after uploading)

Staff: Feel free to add more links to this list if you feel like it and people feel free to post any below so they can be added. Try to stick to major resources and softwares for general use, though, such as tutorials, manuals, wikis, etc.

It's actually 262144 colors. The screen internally uses 18-bit color. But TI uses the 16-bit mode because it's easier. Nevertheless, it is entirely possible to write an assembly program to produces 18-bit color, and in some circumstances (e.g. dynamic generation of color graphics) it is probably preferable to do so, because it supports an option for writing the red, green, and blue values separately.

Oh nice I didn't know about the CSE-compatible TilEm. If someone finds it I will try to add it And thanks DrDnar.

Anybody knows what tools are available for Z80 assembly programming? Has Wabbitcode and DCS SDK been ported to the new calc yet?