[Alberto_Kravina]

WOW! Cool explanations jdurg !

[pantone159]

I agree with all of jdurg's comments, so I'll add some props for some others:

Neon - Lovely color in gas discharge tubes.  Neon was first discovered by its spectra (like many elements, thallium included), so the first sign anybody had of this new element was the sight of that intense red-orange glow.  I think it is cool to imagine that discovery.

Iodine - Fairly cool looking crystals, and very pretty violet vapor.  Besides, its by far the easiest halogen to handle.

Mercury - Pretty obvious, too bad it is so dangerous.

Iron - Ferromagnetism is a neat property (although Fe is not alone), forms lots of colored complexes so it is fun to experiment with, tremendously economically important, plus we need it to breathe.  (Another one of those colored complexes.)

Copper - I think this might be the prettiest metal, plus it has some of the prettiest minerals (e.g. malachite and azurite).

Plutonium - Many brightly colored solutions (with different complexes and oxidation states), bizzare mechanical properties (density changes of 30% or so, strange electrical and thermal conductivity, many different crystal structures, solid Pu floats on liquid unlike almost everything else.)  It holds a huge amount of energy, hence its dark side, which is already responsible for 100,000 or so deaths  
Happily and sadly, I can't seem to get a real sample.  The North Koreans won't answer my emails.

Cesium - jdurg already mentioned this, but liquid Cs is just so cool, I'll mention it again.

[constant thinker]

I'm sure quite a few people here know this, but the Washington Monument (Washington D.C., United States) is capped with aluminum instead of gold because at the time aluminum was a heck of a lot more expensive than gold.

Just a cool little fact. If anyone knows about aluminum purification it uses up a lot of electricity. I'm surprised that it's cheap.

[ATMyller]

I've always liked elements in platinum group. Not because they are shiny and expensive, but because they're all dense, solid and nearly inert.

Iridium is my favourite. It's the most corrosion resistant metallic element, it's dense, very hard and those few salts it makes are nicely coloured. Plus it has a cool name.

[Chrataxe]

Call me cheesy, but I'm gonna go with Oxygen.

[mz4000]

This isn't an element but my favorite is Tri Nitro Toluene.  (TNT)

[P]

I think we have already had this discussion before, or it may just be de ja vu -

Anyway -  definately Sodium  (espessially when chucked into water)
  and maybe magnesium (when put in a bunsen)

[Ψ×Ψ]

This is SO not fair for carbon fiends like me!  Favorite type of compounds, maybe?  Since there are so many?  (I'm kinda partial to arenes.) 
Second place is split between silicon and oxygen (O₂, preferably singlet state).

[constant thinker]

Maybe we should add compounds to this too. Lately I'm starting to like carbon more and more. Mainly because esters are interesting in there fragrances, and not all that hard to make. Getting the chemicals can be though...

[dfx-]

Fluorine....no particular reason..

I'd like to take this opportunity to change my mind completely.

Silver is now my favourite element, since that's what my final year research is on - electrochemistry & silver/platinum/gold nanoparticles.

[mdlhvn]

I love gold. It is very noble

[jdurg]

There's something about ALL of the platinum group metals that just begs for attention.  Whether it's the rarity of it, the beauty of it, the nobility of it, or the density of it, all of the PGMs are a joy to hold.  As each day goes by and the price of it continues to rise, however, rhodium is taking a special place in my heart.  Especially since I have a sizeable 10-gram button of it. 

[P]

This is SO not fair for carbon fiends like me!  Favorite type of compounds, maybe?  Since there are so many?  (I'm kinda partial to arenes.) 
Second place is split between silicon and oxygen (O₂, preferably singlet state).

Yes  -  as a diamond it is lovely!     

[Glaudge]

man.......i gota lot of favorites,
 elements: magnesium right now is best, then osmium, ununhexium,ceasium (big explosion in H2O
) Titanium, Tungsten
simple compounds: TiO2 H2O(gotta have it) C2H6 AlO, and most all nitrates.

[jdurg]

man.......i gota lot of favorites,
 elements: magnesium right now is best, then osmium, ununhexium,ceasium (big explosion in H2O
) Titanium, Tungsten
simple compounds: TiO2 H2O(gotta have it) C2H6 AlO, and most all nitrates.

You'd be amazed, but Cs in water doesn't really produce a massive explosion.  Cs is denser than water is so it will always sink to the bottom.  As a result, a lot of the H2 it generates gets stuck under the surface of the water and is unable to explode.  Honestly, Sodium and Potassium are the two best alkalis to see explode in water because they are "light" enough to remain on the surface where the H2 and O2 can mix and ignite.  Sure Rb and Cs will go "boom", but with the same mass of Na or K you'd see a MUCH bigger explosion.