FINAL UPDATE: Google has killed most of the workarounds listed below.  The best solution I have found so far is this Firefox plug-in: iGoogle Tab Remover I have pretty much relegated myself to the fact that if this workaround fails that I intend to find a new home page portal.  Netvibes sure looks pretty awesome.

UPDATE 6/3/09: Well the time has came and google fixed the ig?gl=all workaround.  http://www.google.com/ig?hl=all is similar to the ig?gl=all trick but I would imagine it’s days are numbered as well, and your best bet would be a firefox or greasemonkey script.

EDIT: You can still do all the stuff I mentioned below, but if you are extra lazy and just want a single Firefox extension to kill the sidebar, I made this for you:
Sidebar Collapser

So if you are a Firefox user like me (and I hope you are), and hate the new iGoogle tabs on the left (and I hope you do), then I think I’ve found the best solution to rid yourself of them.
First, you will need to install a Firefox extension called Greasemonkey available for download here:
Greasemonkey
Then after that is installed install this greasemonkey script available from here:
iGoogle Sidebar Collapse
This is my version of Rocketmaster script. I changed the side tab collapse arrow to match the green of the Tea House iGoogle theme I use. I also set it to work on more addresses than Rocketmaster’s version. If you want to change the color of the arrow that gets rid of the side tab then once the script is installed, go to Tools; Greasemonkey; Manage User Scripts; Select the iGoogle Sidebar Collapse; and select Edit. Find this block of code:

#iGoogleSidebarSwitchButton.closed {
border-left-style: solid;
-moz-border-left-colors: transparent green;
}
#iGoogleSidebarSwitchButton.opened {
border-right-style: solid;
-moz-border-right-colors: transparent green;

Transparent green is the color, change both instances to what ever color suits you
Hope this helps!

If you have the adblock extension for Firefox, you should be able to completely kill the whole left sidebar with this filter:

google.com#TD(class=leftborder)

I’m trying to cobble together a Greasemonkey script that will sort of hobble tabs back up top for the people who only really use one tab. Check back later for that.