We reported about the - $79.99 after rebate.
T-Mobile Sidekick at Letstalk - $99.99 after rebate.
T-Mobile Color Sidekick at Amazon - $49.99 after rebate.

Of course you need to check which on of the above offers the right plan for the sidekick phone deal.

Danger has on their web site rebate coupons that promise to bring the price down to $34.99!

The T-Mobile Sidekick is a small (4.6x2.6.x1.1inch) versatile communication device with its unique swivel screen. A large color screen that flips open to reveal a full QWERTY keyboard. The Sidekick features a wide range of AOL-based online services. Sidekick also provides Web browsing on T-Mobile's national GPRS network, which includes access to Sidekick forums, contests, and a personalized homepage. It also provides up to 6 MB of email storage, and users with AOL accounts (not included) can sign on and access, manage, and set up as many as three different POP3 e-mail accounts and use AOL Instant Messenger to chat with anyone on your AOL Buddy List.
The device also includes a customizable address book that lets you give favorite contacts their own ring tones, blinking light, and their own caller ID picture, taken with the included attachable camera.

T-Mobile Sidekick Features:

Size - 4.6 x 2.6 x 1.1 inches 
Weight - 6.02 oz. 
Battery - Lithium ion 
Talk Time - 3.5 hours 
StandBy Time - 60 hours 
Flip screen to expose QWERTY keyboard 
Keyboard - QWERTY style, 46 keys, dedicated number keys and @ symbol. 
Screen Type - Transflective, TFT, 16 bit-color(65,536 colors) 
Screen Size and Resolution - 2.6" diagonal (116 mm), 240 x 160 Pixels 
Notification Methods - Multicolor flashing scroll wheel, polyphonic alerts, vibration motor, Notification banner & icons 
Ring Tones and Alerts - Polyphonic 12-voice MIDI Synthesizer, 18 Ring Tones included 
Memory - 32 MB RAM, 4 MB Flash 
Web browser - Real surfing on virtually all of your favorite sites. 
Up to 6 MB of storage space for your Sidekick mailbox. 
E-mail - Set up as many as three POP3 e-mail accounts to deliver mail directly to your Sidekick. 
Customizable address book allows to give your friends and family custom RingTones, blinking light. 
Full-feature mobile phone - Chat it up! 


Additional Features:
AOL Instant Messenger™ Service (AIM®) 
AOL® E-Mail 
An organizer! Synchronize it all wirelessly to your desktop interface. 
Game arcade - For the fun at heart, blow it all off and play an addictive arcade-style game