I feel compelled at the moment to add my own list, but... It ain't easy.
1. Oblivion and Skyrim have tied. I blame my characters. I'm too attached to two of them (one from each game) to decide. Seryna is forcing Oblivion to the top while Vulom is pushing Skyrim to the top.
2. Black and White. So many years put into that... Shame it doesn't work well with newer systems. I usually go with the evil god + good creature combo. My main being Azaren (mostly good, but went mad after Khazar's banishment and the theft/torture of Quinn by Lethys. Regained his sanity after the defeat of Nemesis and corrected his evil ways) and his giant rainbow turtle Quinn (good, but very effective in combat. Never quite mastered feeding himself, though... At least he doesn't eat my people, unlike that stupid "good" wolf I have on my laptop. Ugh). Edit:
Quinn in his current form, for those who might be interested in seeing a giant rainbow turtle. I hate how the draw distance is stuck low.
3. Rise of Nations. I mostly tend to use it as a sort of sandbox, but I had multiple games against family members/friends on the LAN. The music tends to get stuck in my head whenever I do play it.
4. Black and White 2. Ye Gods... The cities I build are ridiculous. I've modded the tribute required to purchase things so I can buy everything on the main tutorial land and the first "real" map against the Norse. In my current playthrough (can't remember the name), the city on the main tutorial land is probably around 2000 people (maybe? I can't remember) and covers a good chunk of the island. I'm trying to grow a big forest on one side, but my people keep stealing my trees. Edit #2:
The city in question. I was mistaken, though. It only contains closer to 1500 minions and covers most of that end of the island. I think I was confusing it with a different city I made at some point.
5. The first three Spyro games have also tied with each other. That would be... Spyro the Dragon, Spyro II: Ripto's Rage, and Spyro III: Year of the Dragon. I still play them on my PS1. I've played some of the ones on PS2 as well (Enter the Dragonfly? I think that was the name of one of them... The others are the newer series. A New Beginning and something about an Eternal Night. I have never been able to finish those three), but they are nowhere near as good. Enter the Dragonfly (assuming that is what it's called) lags like hell on my PS2 and the newer series changes the game so much they might has well have changed the names of the characters 'cause it ain't Spyro anymore. They aren't too bad if you like killing [&@%!], but... They can't hold my attention for long.
Honorable mentions...
6. Zoo Tycoon and Zoo Tycoon 2. I recently started playing the first one again on my laptop (since it's one of the few games that thing can run) and apparently I can spend hours playing it without realizing that much time has passed. I prefer the graphics of the second one (and the added Zoo Keeper mode. Just creating a "map" for exploration was more fun sometimes than actually making a zoo), but they're both fun. Shame my current PC can't run Zoo Tycoon 2 without lagging horribly (which is kinda strange since my old one ran it just fine, even though it was weaker).
7. Some of the Crash Bandicoot games. I haven't played many, but the racing games (Crash Team Racing and Crash Tag Team Racing) stand out. Along with Warped, Crash Bash, and The Wrath of Cortex.
8. MediEvil 2. Never got to play the first one and my time with the second was limited considering my disc broke. It was fun, but I remember certain levels were extremely frustrating to child-me. The [&@%!] carnival with the fat bearded ladies, laughing and screeching... The Freakshow, I think. The pumpkin monster level (Kew Gardens?) was another. Actually, I think I could list most levels as frustrating considering I had no idea what I was doing back then. I was recently watching a playthrough for it and I found myself going, "Really? That was it? [&@%!], child-me was an idiot. I still am, but at least I'm not that stupid."
9. Black and White 2: Battle of the Gods. Technically an expansion for Black and White 2, but it runs like another game. Might as well be another game. The Aztec god has a nice growl for a voice (I find myself wishing Alduin had sounded more like him) and some of the incidents on the Norse land are comedic gold, but... The game/expansion only has three lands. Four if you count the bonus (I never did like that land). It doesn't take long to beat at all.
10. Morrowind. This one could have potentially been higher, but it suffers from the exact opposite problem of Skyrim and Oblivion. I haven't been able to create a character I like for Morrowind. I've had multiple characters over the years, but there is so much of the game I haven't done because I haven't had a good enough character to keep me playing. I like it, but without a good character, I can't play for long. Even just exploring can get a little boring after a while.