One of the cards I've done many times is Birds of Paradise. Here are some of them paired with their test sketches I've made for each one.

This version is winter themed:

Another winter themed version that I rejected and was left unfinished.

A Nouveau version:

 The following two were painted on promo foils from M11:

This one was made for an altered card contest from Mtgsalvation.com. The contest's challenge was to paint a card inspired by a song, which in my case was Bird of Paradise by Snowy White. It finally won the first place :). This is the said contest http://forums.mtgsalvation.com/showthread.php?t=475538.

The reference photo I used:

 And this the song by Snowy White that inspired the card:

Since Halloween is near these are all my related alters:

 And the sketches I based them on:

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Here is another fan art group of alters I've done, this time the theme is Thundercats:

The Sword of Omen as a Jitte:

Cheetara as a Stoneforge Mystic:

Panthro on a Beast Within:

A Command Tower altered into a Cat's Lair:

Some reinforcements arriving:

Mumm-Ra as a transforming Delver of Secrets:

And a Swamp made into Mumm-Ra's pyramid:

The only sketches I've made were for Cheetara and Panthro, the rest were drawn straight on the cards.

These two Heartless Summoning are fan art themed after Kingdom Hearts with tons of Heartless. 

Version one:

And version two:

Another 4 of the first version I made for a set:

 This is the sketch for the second version before I transfer it with carbon paper on the card.All 5 cards with the first version where drawn straight on the card.

My latest attempt on creating some original art nouveau style cards:

And the sketches I made beforehand:

Being a horror movie fan I couldn't resist not to paint this group of cards.I used a still from each movie as reference.

It (1990).

Nosferatu (1922).

Sweeny Todd (2007).

The Woman in Black (2012).

Ju-on: The Grudge (2002)

 The Ring (1998).

Sometimes I paint a group of alters themed after something specific.The first group I painted this way with original fan art was these 5 cards themed after the Legend of Zelda games.

A Stoneforge Mystic with princess Zelda and the Master Sword as they appear in the The Legend of Zelda: Twilight Princess.

For this I painted Agahnim and Zelda as they appear in The Legend of Zelda: A Link to the Past.

For this Plains card I painted Zelda from the latest game, The Legend of Zelda: Skyward Sword.

The next two are based on screenshots from  A Link to the Past.

 And this Swamp has Midna from The Legend of Zelda: Twilight Princess.

These cards are also related with the Zelda games but they were painted before and after the previous group with various Link fan art.