There is a woman named Arvena Thelas in the town of Anvil who has four rats 
in her basement (the same
as the first Fighter's Guild quest). If your level is high enough that rats 
do not cause you significant damage,
you can break into her house, annoy the rats by punching them (or casting 
drain fatigue spells if your punch
is too strong), then letting all four rats attack you while occasionally 
casting a heal spell. This is also useful
for raising your Block skill, and is much easier than repeatedly causing 
summoned monsters to attack you.