Collection of SharePoint webparts - Sites and places

 ‎http://www.dundas.com - Primarily chart and KPI webparts  

http://www.amrein.com/sharepoint - A collection of various useful webpart, Image Rotator etc..

http://www.boostsolutions.com - Administration, BI, Collaboration, Content Management and Security

http://www.bamboosolutions.com - Many useful webparts and solutions available to 2007, 2010 and 2013

http://www.virtosoftware.com - Administration, BI, Collaboration, Content Management, Workflow, Bulk Operations and Project Management

http://www.pentalogic.net - A small collection of webparts you might find useful. Team Time - if you looking for a Punch Card/TimeSheets solution

http://www.kwizcom.com  - Many useful webparts and solutions available to 2007, 2010 and 2013

http://www.lightningtools.com

http://www.layer2.de

http://www.codeplex.com - Opensouce projects/webparts, with very different functionality, workflow add-ons, powershell scipts ect...

http://www.harepoint.com 

SharePoint, Show 2 or more webparts side by side

It can be very useful to be able to place 2 webparts side by side in SharePoint, especially if you don't have the option to add a custom page template or don't know how to. Also in SharePoint online, you possibilities can be limited, and this might be a good solution. Just add a table to you page and place your webparts inside the table columns:

Taken from the source link below:

How do we do it?

• enter in Edit Mode;
• choose a location for the table;
• insert a table with n columns and n rows (depends on the number of web parts);

If you already have some web parts in the page just drag & drop them in the table.
If not, click in a column and then insert the desired web part.
  

Source: Alexandru Dionisie