I run an old DotNetNuke 2.11 website that uses the NTForums module from Active Modules, Inc. NTForums is actually outdated and the current product has be rebranded as Active Forums. Active Forums supports DNN 3.1, 3.2, 3.3, 4.0, and 4.3. The only reason I haven't installed the upgrade yet is that I keep having trouble with the DNN upgrade itself (not the module upgrade).
Last night I had some trouble with a sql injection (fun times!). Luckily, the injected script was basically harmless, just annoying. It had the result of redirecting anyone who came to my site to Google.
On the other hand, Active Modules support was spectacular. ActiveModules support, at 2 am EST (yes, they are on the east coast too), responded to my query within a few minutes. I'd simply asked if they could tell me what tables to look at in the db in order to find the cause of a problem that was created as a result of the injection. They went above and beyond and offered to connect to my database and find the problem themselves. They did, and even repaired it for me. Wow! Now that is first class support. If you read the forums at ActiveModules.com, you'll see that this is not out of the ordinary, and they have a very loyal user base. If you're in need of forums for DNN, look no further.