With all the third party mod vendors out there these days, I thought it would be handy to have a list of the major mod vendors and a bit about what they sell. Please note that I am in no way playing favorites here, nor am I affiliated with any of these vendors. I am keeping the post locked, as this is not the place for rants/raves/questions/advertisements, it is meant as a resource only. If I have missed a vendor, or if you are a vendor and wish to be listed, please send me a PM.
In no particular order:
BCS Engineering - Kind of the central clearinghouse of mods - they sell both their mods and many of the other vendors as well.
Firetank Software - Home of the famous Marketing Manager Pro
WebSiteCM - creator of the EZ Checkout, EZ Upsell and CDSEO Pro url mods, as well as some other excellent mods
AlteredCart - some 'must have' mods here including the one page checkout, Smart Search and On Sale mods
SafetyNetWeb - home of the famous DSEFU, as well as Auction Manager and Create A Sale. Some of the best customer service in the business.
XCartMods - Phil is the 'menu man' with some great CSS menus for X-Cart as well as some other unique mods
7Dana - some of the best X-Cart skins around
MercuryMinds - Offers modules like One Page Checkout, smasher-advanced search engine, X-Cart Mailchimp integration & many more
WorkingManSoftware - a great endicia integrator for X-Cart
RubyMods - GeoIP, currency and FedEx tools
Atandra - while not really an X-Cart mod, their T-Hub tool integrates X-Cart, Quickbooks and all the major shippers
MagneticOne.com - X-cart modules
aheadworks - X-cart skins
XCartMod - quick search, product option mods and more
Freeportway - modules that integrate Order-Entry and ERP systems like Mail Order Manager, OrderMotion, etc. to X-Cart
phpmagicscripts - Free X-Cart mods.
SingleFeed.com - Export mod allows X-Cart merchants to export their products into a SingleFeed format which then is submitted to all the major comparison shopping engines.
Cart-lab.com - Various X-Cart Mods and skins
IronShop.fr - French manual translation for X-cart
CartOnSteroids.com - X-Cart modules and add-ons
The xCart Store - Creators of xBanners & Predictive Search modules - plus Modern Living template.