I'm currently in the process of developing a suite of VST plugins but I don't want to go for the same old effects everyone uses. I already have an imitation 303, a versatile analog-style synth and a semi-realistic drum synth, but I want to do something original. Any ideas?

can you use vst plugin to control sequencer? if yes - try doing some computer generated composition... can be fun

A good vocoder, where both modulator and tone signals are VST inputs, and the user gets to set the number of bands and their sensitivity.

hmm... I was thinking of a vocoder. It could be quite CPU intensive with all those filters, but I'll have a go. Another idea with vocoders I had was to have a vocoder which pitch tracked the input, quantised it to the nearest semitone, synthed a carrier signal, then did the vocoding, but that could take days of work.