you missed a few: 'count' 'include_entities' 'from' 'to' and 'source' 

I found that 'from', 'to' and 'source' work both in query strings (eg"q=from:drevicko") and as url parameters, similarly to 'since' and 'until'. This doesn't seem to be documented at dev.twitter.com

with the tests I did, 'show_user' was ignored