3D TV Ready? Or What?

At a minimum, both the source and display need to support the 3D Blu-Ray spec in order to watch 3D movies.

Short answers:
- Unless you use a PS3, it's almost guaranteed you'll need a new Blu-Ray player.
- "It depends" on the TV - some TVs can be outfitted with a "kit" to make them work with 3D, but it's not yet clear which TVs will be covered
- All indications are that today's HDMI 1.3 cables do have enough bandwidth to provide full 1080p 3D to each eye.
- Receiver doesn't need to be updated provided you bypass the receiver for the video feed and go directly from source to display.
- As for content, there will be some, no doubt, but as with all formats, it takes time to get a nice selection.
 

Longer Answers (for those that like to read)
 
Source (Blu-Ray player)
It's still unclear whether or not today's "2D" profile 2.0 Blu-Ray players will be firmware-updateable to 3D.  Initially, it was reported that HDMI 1.4 compliance (a hardware spec, not a software spec) would be required in order to provide full-HD 3D (1080p to each eye).  However, Sony has since stated that the PS3 (which is HDMI 1.3) will support the full 1080p 3D with a simple firmware update at some point in the future.  No similar announcements have been made regarding any other currently available 2D Blu-Ray player.  It's very likely that the PS3's more powerful processing architecture is what makes this possible, and if that's the case, you should count on having to pick up a new 3D Blu-Ray player.

Display
In order to see the 3D effect from 3D Blu-Rays, you will need to use "active shutter" glasses.  These are not like the cheap, polarized glasses you get at the theater for RealD movies.  These are battery-powered glasses with LCD screens that "flicker" in sync with the TV.  They alternate from left to right so that each eye sees only the field that is associated with that perspective.  The synchronization with the TV is achieved using an IR beam from the TV to the glasses.  This effectively "marries" the glasses to the TV - much like how remotes from one brand of TV don't work with other brands of TV, the active shutter glasses from Samsung will not work with a Panasonic 3D TV.  Some TV manufacturers will offer "kits" that are essentially IR emitters that will provide the synching capability with pairs of glasses.  The glasses aren't cheap, either - roughly $150 a pop.  There is at least one manufacturer that will offer "universal" glasses, but at about the same price point.

So some of today's TV's can be converted, but it's unclear exactly which models and how much it will cost.

^^^The only sets that can be converted are certain Mitsubishi and Samsung dlp rptvs--Mits makes a converter box that will work with both sets.  The box is relatively cheap (150ish?)

The only legacy player that can be upgraded is the PS3.  Sony has their new 3D player on store shelves now but it will require a firmware update before the 3D will work.  Any 3D player will work with any 3D tv.

The IR synch emitters are built into Samsung and Panasonic 3D sets.  Sony will offer one line of 3D sets with the emitter built in, another that requires an emitter kit.  Rumor is that Vizio will have Bluetooth synch rather than IR.

Glasses are tv brand specific now.  Xpand is offering universal glasses. 

DirecTV has announced it will carry three 3D channels starting around June and that a firmware update will enable 3D on most newer boxes.  Due to bandwidth constraints it's rumored these will be downrezzed but still should look very good.