You can use LaTeX (codecogs rendering) in the Blogger text/HTML editor directly.

http://userscripts.org/scripts/show/64270
LaTeX for Blogger w/ Undo in the Updated Editor
For a description/install of this tool and comparison with other methods to post equations, see: http://ex-ample.blogspot.com/2011/07/mathml-chromefirefox-and-best.html


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here: just a test of the use of LaTeX for Blogger 
("64270.user.js" as extension of your browser).

4 steps:
1) I write this latex code:
e = \lim_{n\to\infty} \left(1+\frac{1}{n}\right)^n


Just a comment: if i write this LaTeX code between "slash(" and "slash)", MathJax will transform and render the equation. Verify in "edit HTML" mode that your LaTeX code is clean (put in div-tags). See the result:

\( e= \lim_{n\to\infty} \left(1+\frac{1}{n}\right)^n \)

With this post you can see than we can use Mathjax rendering and the www.codecogs.com rendering used by "64270.user.js" together without problems.
2) I put double$ between this LaTeX code.
3) I click on the LaTeX button :

4) click "publish post"

----------------------the result is: