Below are a few links to some game art from various games and websites that would be usefull for FRUA. Most have been discussed before, but I've found actual links for some of them,plus I'm working on playing a few and grabbing screen shots as I play.
RPG Maker - If you just do a general image search on Google or Yahoo you'll be flooded with tons of items. But if you get specific, some nice things turn up. Do a Yahoo image search for "rpg maker lion" for instance, and a couple of nice sets come up, as well as a nice tiger set a little lower down.
The rogue-like games use tile sets and there's many different good ones out there. An image search of Rogue or Nethack with "sprite" or "sprite sheet" added turns up some nice finds.
Heroes of Might and Magic 1-3. These would be nice combat icons if adapted. All of them are available with the different frame animations athttp://spritedatabase.net/system/pc
Might and Magic series - the first is too basic to be of much use. For Two, the SNES version is supposed to have improved graphics and I'm going to check it out when I can. I remember enjoying 3-5 when they came out, but looking at them now, most of the creatures seem a bit silly looking. Sprites for 3 though 4 can be found at the RPG Shrine link below. Six through 8 can be found at the sprite database link site above. These look like they would work well with FRUA.
The link above also has many other games to look over with good artwork. The Shadows over Mystara game has a nice Gnoll for example.
Wizardry - There's already a few links to some of the Wizardry games here. For 1-3, 5 and 6, the SNES versions have good sprites. The sprites for 5 can be found here - http://www5a.biglobe.ne.jp/~outlaws/wiz_rpg/monster01.htm
The sprites for 6 can be found here - http://www.pekori.jp/~emonoya/monster/6/sfc6m_01.html
For 7, though I haven't tried it, I think you can get the sprites by using the Cosmic forge editor that's available - you might be able to get usable art from 8 as well with this.
Sprites for a few games like Final Fantasy 6 can be found here - http://www.rpglegion.com/sprites/index.htm
Eye of the Beholder - Dungeon Hack has already been done. Sprites for Eye 1 and many other games can be found here - http://www.spriters-resource.com/pc_computer/adndbeholder/
I haven't found sprites for Two, Three or Lands of Lore. I might have to play through these again and grab some sprites.
Bard's Tale - most versions have EGA or worst graphics. The Sprites for one of the better versions, I think Amiga, are here - http://shrines.rpgclassics.com/pc/bardstale1/enemies.shtml
This site also has art from many other games like Shadows over Mystara and the Genesis version of King's Bounty.
I couldn't find anything for Two, Three of Dragon Wars. I'm doing a quick playthough of BT2 for Amiga right now and screen capturing as I go.
I've got quite a few old RPG's sitting on the shelf that I've never complete or even started. I'm finding FRUA is a good excuse to get them out and try them again. At present I'm going through BT2, which I did finish way back when it first came out, and ISHAR 1 which I had never got to.