www.mvcool.com is a good place for third party modules provided by various developers. You can buy modules for configuring coupons, changing checkout options, more control over the miva database.. etc.
Have fun customizing your store

http://truxoft.com

great modules for miva that I'm using here now.....


-Wiley

While I have found that mvcool has a large quantity of quality modules, viking coders maintains alot of the hard to find modules out there for Miva Merchant, so just in case:

http://vikingcoders.com/

You can review modules by different vendors at my miva merchant modules directory listed below and also get free consultation by email. It has the largest database of modules available anywhere. I don't know what the "ahem" is all about, but If you search first at Miva Central, you won't see plenty of modules available since not every module developer lists their modules with them. Biggest problem that people have when they contact me is that didn't know that a better module was available.

Jason
JMH

Ahem: the first place to look is generally MIVA CENTRAL. basically, you will find most anything you need there. If you can't find it there, try searching over at google.com for "Miva Module _____ _____" filling in the appropriate keywords like Coupon Processor. That's all you really need to do.