Jumping on the bandwagon of chemistry "favorites" lists - mine comes from the perspective of a phytochemist... see also Chemjobber, LabMonkey4Hire, The Boiling Point, LJKBoerner, Sciencegeist, and others...
1. Realizing that the compound you finally isolated is, in fact, new
2. Realizing that your new compound is bioactive
3. Discovering that someone has synthesized a compound you discovered
4. Sephadex LH-20: the best stationary phase ever
5. Seeing liquid oxygen condension out of the atmosphere and dripping off the liquid helium port when doing a cryo fill for the NMR
6. Plant collection trips
7. Ion traps that fragment a compound just right & accurate mass when you need it.
8. Butanol and toluene when you need to evap water faster
9. Getting the solvent system right the first time - and nailing the pure compounds.
10. Training on a 300 MHz, and then moving on to a 500
11. a new HPLC column
12. fixing my own glassware