Visualisation of long read RNA-Seq splicing
DNASTAR's software is for purchase, but high quality. GenVision Pro does genomic visualization, including Sashimi plots.

Edit: not sure why this answer is being downvoted, unless it's because the software isn't free. OP has tried IGV and SeqMonk, I mentioned an alternative he might not have heard of.

Here is a video demonstrating the use of Sashimi plots in GenVision Pro:

http://www.dnastar.com/t-support-videos.aspx?video=YJvcERoSIsg