Ask Mr. Smarty Plants

Poisonous Plants of North Carolina

Cornell University Plants Poisonous to Livestock

Canadian Poisonous Plants Information System

Universiy of Pennsylvania Poisonous Plants

Texas Toxic Plant Database

University of California-Davis Toxic Plants

Some of these are geared toward livestock and others are more for humans.  You can also find specialized databases for pets (e.g., ASPCA Poison Control Center).  In fact, you can find several sites with lists of plants toxic to rabbits by Googling "poisonous plants rabbits" (e.g., Rabbit Advocates Toxic Plant List and 3 Bunnies Rabbit Rescue).  Although many of the lists are alphabetized by common name, you are usually better off searching by the botanical, or scientific, name where possible—common names vary by region, botanical names are more universal and rarely variable.  Here are the scientific names for the plants you mentioned and some information I found for them.  I did not search all the databases—in particular, not all the rabbit toxic plant lists.

Anagallis arvensis (scarlet pimpernel), listed on the University of California-Davis database as of 'Minor Toxicity' and listed on the Canadian Poisonous Plants Information System as potentially poisonous.

Euphorbia maculata (spotted spurge), several Euphorbia spp. listed on the UC-Davis database as of 'Minor Toxicity'.  E. maculata is listed on the Poisonous Plants of North Carolina database as being mildly toxic.

Cyperus esculentus (yellow nutsedge) is not on the UC-Davis list, nor on any other list that I looked through.  You should check all the toxic databases, especially those specific for rabbits, to see if this species occurs.

There are many Oxalis spp., some native and some not.  You can see the possibilities for species in California by looking at the maps on the USDA Plants Database page.  Oxalis spp. is not on the UC-Davis list, but is listed on the Poisonous Plants of North Carolina as mildly toxic and 3 Bunnies Rabbit Rescue lists Oxalis as toxic.