An interesting thread Big G, after careful consideration my top 10 ranked according to time savings would be:
1. MULTI-SECTION - a terrain & pipework longsection generator. Basically I draw a pipe route on a digital map using a polyline, select it and voila, a series of drawings each showing a plan (aligned to the pipe-route) and a corresponding long section beneath. This little baby can generate a dozen A1 drawings within a minute.
2. MAP CONVERSION - this one automatically reconstructs missing symbology in digital map data imported from a proprietry GIS system. This one doesn't sound very interesting but it saves many hours of tedious manual editting.
3. TERRAIN MODELLING - this is a combination of numerous 3D ground modelling routines such as TIN creation, breaklines, surface drapes & burrying etc.
4. RESAMPLE OBJECT - this routine effectively traces over existing objects using a user-defined number of vertices. I use this to remove excessive polyline vertices and to convert arcs, circles & ellipses to polylines.
5. REVERSE OBJECT - Does what it says on the tin.
6. BATCH LISP PROCESSING - this little app will allow me to run any lisp routine on a whole folder of drawings, including sub-folders if desired.
7. AUTO MATERIAL ASSIGNMENT - this one allows me to select a pre-dined material (concrete, asphalt etc) from a drop-down list box and then apply these by object, layer or by a bounding polyline.
8. DRAW ORDER BY LAYER
9. COPY OBJECTS TO LAYER
10. ANI-MATE - this is a sweet little animation routine, it's been around for a decade now and looks suspiciously similar to the one introduced in Acad2007.