I have gotten a lot of soulbound cards since it started. Here are the ones that usually use in the silver and bronze leagues.
Fire - I got Ferox Defender, Firecaller, Pyrewatch Devil and Eternan Brune. I rarely use them because I can't find good synergy in my team with Tarsa as summoner.
Water - I got Swamp Spitter, Coastal Sentry, Riverboat Captain and Pembrook Nymph. I use Swamp Spitter and Riverboat Captain a lot as they work well with Kelya. I would love to get Kulu Mastermind and Noa the Just. I can see good synergy in both cards.
Earth - I got Fungus Flinger, Terraceous Grunt, Madcap Magus, Thane Newsong and Lobb Lowland. It's fun to use Lobb Lowland if you have Quora. She just wrecks in the lower leagues. Terraceous Hulk seems like a beast. I would love to get that one.
Light - Imperial Knight, Drybone Barbarian, War Pegasus and Franz Ruffmane. I use War Pegasus in my archer team from time to time.
Death - Possessed Puppet, Wily Coyotian, Ravenhood Warden, Usut and Octavia Shadowmeld. I often use Puppet and sometimes the legendary card Usut.
Dragon - I got Kraar Zoc and Hellios Matriarch. I haven't used them that much though.
Neutral - I got Gobson Bomber, Dumacke Orc and Venari Marksrat. I haven't used them that much but I can find some use for the Dumacke Orc for no magic rulesets.
In the silver and bronze leagues, I usually use the water and earth cards. So far, these are the new cards that I can find use and add value to my team. As for the other splinters, I cannot replace the CL cards I already use. On the other hand, I'm hoping to level up my summoners to be able to use my Gladius cards.