What is a good video converter to convert videos to 3gp that will work on my Nokia 6300?

You can try Cucusoft DVD and Video converters suite which includes Cucusoft Ultimate DVD and Video Converter Suite. It is the best all-in-one DVD and video conversion software converts DVDs and videos to play on almost any portable device including iPod, iPhone, Zune, PSP, video capable MP3 players, video capable mobile phones, and Pocket P.C., etc.

Free Download, Flv to 3gp Software Collection Download.

This article shows you how to Extract audio from Flash video, FLV to MP3(MPEG Layer-3).

Software for 3gp 3g2 video converting, convert any video to 3gp 3g2.

You can free download this software free from here:
http://dvd-video-converters.com/dvdvideo...
Unbiased reviews and side-by-side comparisons of DVD video converter suite give you enough information to research the ins and outs of a particular product:
http://topsreviews.com/reviews/dvd-video...
For mac users, you can choose Aimersoft DVD Converter Suite for Mac:
http://macdvdconverter.com/mac-dvd-conve...
Also, you can google some other software:
http://www.google.com
I always use Tipard Video Converter. It supports the mutual conversion between all video/audio formats, and HD videos. It also can set video effect, set Deinterlacing, trim your video length, crop the play region, merge into one file, customize output settings.
For more informaion and free download from:
http://www.tipard.com/video-converter.ht...
It is easy to operate. Just few clicks are OK.
Here is the specific guide for you to follow:
http://www.tipard.com/how-to-convert-vid...
Hope it useful for you.
I know a good video converter to convert videos to 3gp. It is Aiseesoft Total Video Converter. It can convert video to MP4/MKV/WMV/AVI and other popular formats such as: MP4, H.264, AVI, MP3, WMV, WMA, FLV, MKV, MPEG-1, MPEG-2, 3GP, 3GPP, VOB, DivX, Mov, RM, RMVB, M4A, AAC, WAV, etc with high speed and excellent sound/image quality.
For more information and free download from:
http://www.topsevenreviews.com/aiseesoft...
Step 1: Install and Run the Converter
Step 2: Click “Add File” to add your video files.
Step 3: you can find one format that meets your requirement from the “Profile” drop-down list
After doing the steps above, you can click “start” button to start conversion.
If you just want converter a clip of your video, then you can use the "Trim" icon to set the Start time and End time of the clip or you can directly drag the slide bar to the accurate position.