ReSSA and ReSlope by Adama Engineering (www.reslope.com) can be used to analyze geotextile or geogrid reinforced soil slopes.  ReSSA allows one to analyze more complicated geometries and foundation conditions than ReSlope  Later versions of STABL can also analyze global stability of reinforced soil slopes.  Be careful entering the geotextile data in STABL, obtain a manual to determine how to enter the geotextile data.  There are also other software programs that can analyze the global stability of reinforced soil slopes.

Strata Systems has software called StrataSlope that is geared directly for their product, StratGrid.  It is free and relatively easy to use.  Unfortunately, it's really only applicable to their product.

Also, it is geared for design, not analysis.  Therefore, to use it for analysis you have to adjust the factors of safety until it shows the length of geogrid that you have in the existing slope.

Check out http://www.geogrid.com for info.  You will need to call them directly to have them send you the disc.

Any slope stability program can be used to analize a reinforced slope.  The reinforced area can be set up as a different soil type with a high cohesion.  This will force the failure surface outside of the reinforced area.  

Note that the reinforced area for the stability model does not extend to the back end of the geogrids.  You have to make a proffesional judgement as to how far from the end of the grids you have to be to have a significant impact on the strength of the soil.

In my experience, this method works much better than the geogrid reinforcing lines that some software allows you to add to the stability model.