Except Udyr, are there champions whose R isn't a priority to be acquired at level 6 or level up at 11?
Usually The ultimate of a champion is intended to be his strongest skill that's unlocked at level 6, therefor I wouldn't consider Udyrs R as an ultimate but rather a default skill. Also Nidalee, Jayce, Karma and Elise don't have real ultimates. But those are definitely the champions where you can delay leveling it.
Please note that delaying or ignoring an ultimate is extremely situational and in 95% of the cases it's a lot better to just level up your ultimate instead of another skill. Also In order to delay an ultimate, your second priority spell must show a good increase of damage/scaling/cooldownreduction so keep that in mind (or your ult has to be useless which doesn't happen too often now).
Anyways I'm gonna list some champions where you can ignore or delay your ultimate situationally.
- Fiddlesticks: You can delay your ultimate when playing mid (especially if you're getting pushed), since it's often better to have some extra fear/damage and usually your ult isn't too strong when playing middle. If you plan to roam, teamfight or if you are against a champion with no gapclosers it's still better to pick it up at lvl 6.
- Gnar: You can delay your ultimate for an extra point in W if you see that your opponent doesn't let you smash him into a wall and if there are very few jungle fights going on.
- Irelia: Very situational but you can pick up a point in E where a longer stun saves your life or wins a fight.
- Sion: When playing AP Sion your ultimate is rather Useless. The only reason to pick it up is for extra sustain if you're getting harassed a lot. Note however that this will change with the rework.
- Pantheon: As Marco pointed out in his comment, Pantheon is also a champion where you can delay your ultimate if you don't plan on ganking other lanes (if you play top or mid). An extra point in E will provide an incredible boost to your damage when duelling other champions.
Now these would be all the champions where you could take it into consideration (and of course Jayce, Nida, Karma, Elise) but usually it's better to skill the ultimate so keep that in mind if you plan on skipping the ult. Always think about what will be more useful if you get ganked for example and think about the matchup.
Another example is Jayce. But with him it is the same as with Elise and Nidalee. A boost in some defensive stats. The difference between these 4 champions and Udyr is that they get their "ultimate" at level one where as Udyr does not have an "ultimate". He just has 4 spells he can freely choose. Thus I would say Udyr is the only champion who can get away with not leveling his "ultimate".