Check this shit out:  

There are other browser based emulators out there; this one seems to be the most well-rounded, flexible, and stable.  The game controls can also be re-mapped.  Using XPadder and a XBOX 360 controller works for me, and is almost mandatory IMO.

Some of my favorites:

Haunted Castle, the first of the Castlevania family to make an arcade appearance,  is one I have never played prior.  The site is full of games that were never released in the U.S.  This could waste much of my spare time.