I use a basICColor grey card which has a Lab value of 60, 0, 0. - Adobe RGB of 143. Not cheap, but as someone wrote above, you get what you pay for.http://www.basiccolor.de/english/index_E.htm
Since there website isn't very explicit, here's a link to a reseller......http://www.colourmanagement.net/bc.html
I also use their profiling software which I think is excellent.