Is the tank cycled? Since it's new I wouldn't add any new fish just yet.
Honestly, I would either take the male back to the store or separate him if you want a community tank. In a 10-gallon it's going to be fully stocked once you start getting babies. Guppies breed like rabbits.
I'm not sure which eels you're interested in but I'm thinking maybe you actually mean loaches? A lot of them look similar to eels. A common one is the Kuhlii Loach:
http://www.liveaquaria.com/images/pr...ge/p_89845.jpg
http://animal-world.com/encyclo/fres...hWFLo_Ap4A.jpg
Or perhaps you saw a Bichir:
http://www.liveaquaria.com/product/p...fm?pCatId=1988
If it was definitely an eel then it was probably a Fire or Tire Track Eel. Neither species is appropriate for a 10-gallon. But if you like eel-looking fish then a couple of Kuhlii Loaches might work.
Other good community fish for a 10-gallon that would work with guppies (in most cases) are
neon tetras, white cloud minnows, pygmy cory cats,
cherry barbs, cardinal tetras, and platies (two or three of the same gender). There are a bunch more, those are just a few that come to mind

.
Good luck with your tank!