Hi, I help run an astronomy group (San Diego Astronomy Association) and I think I can help you out - feel free to contact me directly if you have questions.
Right now I would recommend showing off:
The Pleiades (M45) -
http://en.wikipedia.org/wiki/Pleiades_(star_cluster)
The Great Orion Nebula (M42) -
http://en.wikipedia.org/wiki/Orion_Nebula
The Andromeda Galaxy (M31) -
http://en.wikipedia.org/wiki/Andromeda_galaxy
You can also check out the planets - right now Mars is pretty close and bright, but it isn't much to look at through a 4" telescope. You can show off Saturn, but it doesn't rise until kind of late. You should be able to see the rings, but right now they are edge-on.
Depending on where you are located, you may also be able to check out some smaller galaxies and nebula. Also, depending on where you are located, get in contact with an astronomy group and see if you can visit a local amateur observatory. We have a site about an hour from down town San Diego where we have a 22" telescope available for public viewing once a month and we also have public events held almost weekly where we bring telescopes generally around 10" in size (I bring my 16" on clear nights).
Others have joked about using your telescope to point at the Sun - obviously don't do it. Even pointing the scope at the Sun will permanently destroy eyepieces and coatings on optics - and if you happen to look through it, say good bye to your vision. Permanently. However, if you can get yourself a solar filter to put over the telescope, you can safely observe the Sun - which is pretty interesting. You should be able to see sun spots and perhaps prominences with the right kind of filter.
Good luck, and clear skies!
:)