Wow... lots of reasonable responses to your question. As an owner of three Pro-Ject tables including the Expression 11 I would say that Viridian's advise is on the mark. The table is a little dark sounding particularly compared to a Rega. I started out with the Audio Technica 440 (which is a little bright) and found it to be synergistically a good match ---the carbon fibre arm has an effective mass of about 9 grams and the fairly compliant 440 matched the relatively low mass of the arm quite well.
Smart move getting the speedbox as that liitle device provides improved speed stability and elevates the performance of this table even further.
If you desire a richer sound but not quite as detailed on top, the Grado Gold (which I own) is the ticket, but it is twice as expensive as the 440. The Grado people in fact make the Pro-Ject K4 and K6 cartridges. Both these are an easy match for a normally aspirated phono stage (i.e MM phono stage). The AT sells for about 90, the Grado about 180. I also own the Shure 97 and The Denon 110 103 and 160 which are great cartridges but seem to work better on other tables such as the Rega which has a heavier arm.
Good luck, have fun, and enjoy the vinyl experience.
