Near rhymes (slant rhymes):
* functional (similar sounds, different vowel sounds)
* unconventional
* refunctional (more of a play on words)
Eye rhymes (words that look like they rhyme but don't sound alike):
* consequential
Other options:
* dys- words like dyspeptic, dyslexic, dysphoric (this is more of a word play on the "dys" prefix)
Ultimately, the best rhyme depends on the context of your use.