What are the commonly used self-labeling tags?

Commonly used self-labeling tags include: 

• Tetracysteine (Cys4): Tetracysteine is a 15 amino acid peptide that is composed of a cluster of 4 cysteines. It reacts with biarsenical dyes such as ReAsH (red, based on resorufin) or FlAsH (green, based on fluorescein).  
• eDHFR: Proteins fused with eDHFR or E.coli dihydrofolate reductase can be labeled with fluorescent derivatives of its substrate trimpethoprim (TMP-tag). This interaction is not covalent, however, when a Leu28Cys mutation is introduced in eDHFR, it can lead to covalent binding of the TMP-tag ligand.
• SNAP-tag: SNAP-tag is based on the human DNA repair protein AGT, which covalently binds to derivatives of O6-benzylguanine (BG). A fast-reacting version called SNAPf is also available. 
• CLIP-tag: CLIP-tag is an AGT-based tag that reacts with O2-benzylcytosine(BC) ligands. It is based on the same original enzyme as SNAP-tag. Although both have the same origins, each tag shows specificity for its own ligand with minimal cross-reactivity.
• HaloTag: HaloTag is based on a bacterial haloalkane dehalogenase that binds a synthetic chloralkane (CA) ligand. The standard version, HaloTag7, is the most popular self-labeling tag in Addgene’s collection, with specialized variants extending to HaloTag11.