Kecleon has been my favorite Pokemon since the moment I laid eyes on it. I added it to my Pearl team mostly for mascot purposes. It wasn't until much later that I realized he's an intense fighter. I could probably get through every game in every generation with this Kecleon alone. It's movepool is incredible and allows it to learn a bunch of elemental attacks, all of which are very helpful.
I wasn't expecting much in terms of fighting because of all the negative things I heard about him on Pokemon websites. I'm happy I looked past it though, my little Kecleon is my pride and joy. ^-^
Sentrets are oddly powerful as well. I added one to my team because I thought they were adorable, but it turns out he can really hold his own in battle. I'm thoroughly impressed with this little guy.
I added a Cherrim to my team, very, very recently. I wasn't expecting much, just a cute little Pokemon to have around. I guess a lot of Pokemon rating websites sort of scared me off. I have yet to see this thing faint, he sweeps through battles where all the Pokemon are much higher levels than he is. It's incredible and nothing like I was expecting.