While IPExpert and proctorlabs has the grading feature for their labs, IE is now also the offering of the Poly Lab Assessment. I tried both and i can suggest both of them. While the Poly Lab is quite new, i tried it twice and the results have been interesting for learning. You can generate your own lab, depending on you skills. If you are novice, beginner, intermediate, advanced or expert in the different R&W topics. The lab questions are then generated on behalf of your skills. The difference to a mock lab is, that after you hit the grade button, your result will be generated in 5 minutes by tcl scripts. The mock lab will be graded by a human and you will get comments on your configurations.
The IPExpert labs have been also very interesting and grading has worked well.
You should try a graded lab. You will probably be astonished about how many errors you can make even with a first looking working configuration. That was for me also the most important thing. Since you will overlook many little errors looking at your own configuration. Many things you wont see that fast and the secure and more easy way to have a script grade you. Since it will not be able to overlook missing or wrong configurations parts. Very good for learning also.
If you are working at a Cisco Gold Partner, then you could also ask your Cisco SE for the ASET Labs. They have a grading machine in the back also from labgear.net. There are several different topics for about 4 hour sessions and also currently 6 different full time labs. All labs can be graded. These are very similar to the real labs, although they are not written by the CCIE Lab team from Cisco. But most important thing is, that you will get them for free and they come from Cisco. You can get about 72 hours per month lab time from Cisco. Even if you just want to lab some things out, this is possible on Cisco’s lab equipment.
If you want to get in touch with the real Labs, you can try the Assessor Lab from Cisco. The will cost you about 200$ each. Still only two four hour labs available, but is also good for a try.
Source:
http://www.internetworkexpert.com/ccie-routing-switching-poly-labs-assessment.htm
http://www.ipexpert.com/index.cfm/product/sku/CCIE_RS_Lab_Graded_Assessment
http://www.cisco.com/warp/public/765/download/pep/aset_qualify.html
http://www.cisco.com/web/learning/le3/ccie/preparation/assessor_details.html