I have maps on my site that are more for solo play than mp play.
http://www.dom3minions.com/maps.htm
such as the Tower maps. Or maps with lots of chokepoints.
Also for AI boosting there are NI maps around (No-Independents) which force the AI to fight for provinces but not recruit there. That forces it to use its elite units more. There are also some PI (partial indepents, such as 1 in 10), or BI maps and mods (Better Independents, making cheap flak units too expensive for the AI to use). Or just setting resources lower on your games can force the AI to build more at its castles instead of spending gold in the provinces.
Another setting to be aware is the Independents Strength setting in games. It would seem reasonable that you set it down to make it easy, and up to make it hard. But its the reverse. Setting it up damages the AI more than it does you, and setting the Indepts low creates a rushing game with the AIs hitting you all at once.
The SemiRand program can boost AIs by giving them randomly selected AI builds (so that Caelum gets cold, Ulm gets resources, Mictlan doesnt get scales that kill it in the first 3 turns of the game before anyone even attacks it)