TuniLame

You will be able to configure the color, size, link and link’s target of each button and even add a defaut button for many posts. 
To use it, just take a look on the plugin’s configuration page which contains all the informations and settings for the default button. 
Add the button by using <code>[button color= size= link= target=]text that will be shown as button's value[/button]</code>
Attributes that can be used: 
* color: There is 7 different colors: pink, magenta, green, red, orange, blue and yellow 
* size: There is 4 different sizes: small, medium, large and super 
* link: The link of the button. Example: Your site’s URL http://mysite.com 
* target: The link’s targeted window, can be: blank, new, parent, self or top 
Exemple: <code>[button color=blue size=super link=http://twitter.com/tunilame]Follow me![/button]</code>
Simply add <code>[button]</code> in you posts when you want to use the defaut settings.

CSS3 Buttons

Add coloured CSS3 buttons on your posts using simply a shortcode.

Deblyn Prado

So, you’re tired of people visiting your modern website with an outdated browser and not doing anything about it. Maybe they aren’t “power” users, maybe it’s your auntie running a last century browser trying to see awesome CSS3 animations and transforms. Let the user know that’s an outdated browser, and advise them on a better one.
With this solution you can check if the user’s browser can handle your website. If not, it will show a cool looking notice advising the user to update the browser. It\’ll be up to him/her to decide if he upgrades or not. Don’t force the user!
This plugin is a version of <a href="http://outdatedbrowser.com/" rel="nofollow ugc">Outdated Browser Projetct</a> created by <a href="https://github.com/burocratik" rel="nofollow ugc">Bürocratik</a>

WP Outdated Browser

Show a message if the user using a outdated browser.

CSS3 Buttons vs WP Outdated Browser