Exact opposite to Ruby's CGI.parse method?
If you're using Rails (or don't mind pulling in ActiveSupport), then you can use to_param (AKA to_query):
{ :a => '&', :b => 'Where is pancake house?', :c => ['an', 'array'] }.to_param# a=%26&b=Where+is+pancake+house%3F&c%5B%5D=an&c%5B%5D=arrayto_param handles arrays a little differently than your version though, it'll put out c[]=an&c[]=array rather than just c=an&c=array.