Dwarf- Digger (works REALLY well, also as a self-referential term), mine monkey, butch, squirt, junior, stone jockey, aleblood (due to their unusual tolerance for booze), any disparaging size comment (while not racial, these are a problem for all of the smaller races)
Elf- Dandelion eater (I think this came from Shadowrun), flower-eater, ears, fairy, twanger (Elven stereotype- affinity for arrows), priss, woody (due to forest affinity stereotype), treetard, old-timer, fossil (in fact, any ageist slur that isn't obviously off setting will work)
Halfling- Half-pint, squirt, hairy paw, anklebiter, human jr, any disparaging size comment (while not racial, these are a problem for all of the smaller races)
Troll- Trog (another SR reference), clubby, bridgedweller
Human- Mundanes, banal ones, vanilla, flavorless one, stock, zilch (due to lack of unique features), defaults, hyoooomanz (in an evil sounding voice)
Half %s- Mongrel, mutt, impure, diet ~, ~ lite, and so on...
Also:
this.