If you have an ATI card with Eyeinfinity, you can set your desktop to a single resolution like 3840x1080 and the taskbar extends to both monitors.

What are you running for video card(s)?

No, it don't. It looks like the default Win 7 taskbar only not as pretty.

DisplayFusion is what I use. 

Needless to say, I recommend the Pro version. It will also let you manage your wallpapers and logon screens. Lots of settings and stuff!

With DisplayFusion's Multi-Monitor Screen Savers, you can use your favourite screen saver spanned across all of your monitors, or use a different screen saver on each monitor.

I tried it out and for Open Source it's pretty good. Has some options to control window placement as well as showing the taskbar item on the applicable taskbar or on both. I had an error when I started the program which notified me of a missing dll. The missing dll is a debug dll and doesn't effect the program's operation once you clear the warning box. I also noted that it doesn't scale up for Large Fonts which makes the taskbar a bit "shorter" than the normal one.

 I've tried Display Fusion a couple of times over the last few years but I hadn't stuck with it. Likely due to the fact that I could replicate most of the functions of the free version with a dock.

I'm still using a system I built in 2009......eyefinity wasn't out yet.

my specs

Cooler Master HAF 932
Gigabyte GA-EP45-UD3P Rev. 1.6
Core 2 Quad Q9550 2.83Ghz E0 3.40Ghz OC'ed
w/ Cooler Master V-8
XFX Radeon HD 4870 1GB DDR5
(8GB) 4x2GB G. Skill DDR2 1066
Corsair 750W PSU Single Rail
(3) WD 640GB Caviar Black HDD
(1) Hitachi 1 Terabyte HDD
Samsung 22X DVD Burner SATA
Saitek Eclipse II
Logitech G9 Laser
Logitech M570 Trackball
Logitech HD Pro C-910 WebcCam
(2) Dell 2001 FP Flat Panels (3200x1200)
Logitech Z-5500 Digital Sounds System
Windows 7 x64 Home Premium

I might build a new one if the Black Friday deals are better this year than last year. With current prices I was thinking of a pair of 6850s