alcohol works but it doesn't really dissolve the TIM.

If found this works good.  Yes a ripoff @ $7 for small bottle (good for 10 GPU at least) but it works very well.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835100010

For cleaning up bad thermal paste jobs which got some of the resistors I have found a method which works well.  Using the #1 cleaner in the link above, let it dissolve some of the thermal paste, mop it up with qtips.  You aren't really scrubbing it (which just smears the paste around to other resistors) more using the qtip like a sponge.  It will take 3 or 4 passes but you can get any surface perfectly clean.