What ffmpeg/avconv format and container will Adobe Premiere Pro accept, out-of-box?
Premiere Pro CS5 should be able to import H.264 video, IIRC, however it may be having trouble with the audio and/or container format. With ffmpeg try re-muxing the video stream without the audio:

ffmpeg -i input -an -codec:v copy output.mp4 -an -codec:v copy output.avi


If both output.mp4 and output.avi work then we know that the issue lies with the audio (although H.264 with b-frames in AVI probably isn't a great idea). You can re-encode the audio and keep the video:

ffmpeg -i input -codec:v copy -codec:a pcm_s16le output.avi


If the first command does not work with Premiere, then you may need to re-encode. This is a good use case for an editor friendly, lossless intermediate file:

ffmpeg -i input -codec:v utvideo -codec:a pcm_s16le output.avi


Close Premiere, install Ut Video (scroll to the bottom of the page), open Premiere, and import your video. You can do your editing, and then export to your final format using the crappy Adobe Media Encoder, or export to another lossless file, and then use ffmpeg to provide whatever you need. Alternatively, if you're using Windows you can use Debugmode FrameServer and encode directly with ffmpeg from Premiere. See How to encode with ffmpeg from Adobe Premiere Pro for instructions.

If you need a recent ffmpeg for Windows see Zeranoe FFmpeg builds.