(Formatting and wording is probably way off since this is from memory but I guess that's part of the fun, eh?)
Rituals:
Darkvision
Level: 3 / Material Component Cost: 125 gp
Type: Exploration / Targets: Up to 10 creatures within 5 squares
Time: 10 minutes / Skill: Nature
The target gains darkvision. Your check result determines the duration of the effect, according to the table below. If you target multiple creatures, all gain darkvision, but the duration is divided by the number of creatures (for example, if your check result indicates 6 hours, but you target 3 creatures, each gets darkvision for only 2 hours).
DC : Duration
0-15 : 10 minutes
16-25 : 1 hour
26-35 : 6 hours
36+ : 24 hours
Permanence
Level: 12 / Material Component Cost: Special (see text)
Type: Miscellaneous / Targets: One ritual effect within 4 squares
Time: 8 hours / Skill: Arcana (no check)
One ritual effect of your level or lower has its duration increased to 24 hours. Once every 24 hours, you may spend a healing surge to extend the duration another 24 hours. You can extend the ritual effect in this manner no matter how far you are from it, even if you are on another plane. If the ritual effect is targeting some other creature, then whenever you spend the healing surge to extend the duration, the creature is entitled to a saving throw to cancel the effect.
Permanence has a material component cost 5x the cost of the ritual you are extending. You must spend 5 healing surges when you initially perform Permanence. If another character aids you in the ritual, whoever contributes the initial healing surges must also be the one who spends a surge every 24 hours to continue extending the duration.
Paragon Feat:
PERMANENT ENCHANTMENT
Prerequisites: You must be under the effect of a ritual which is being extended with Permanence.
Benefit: The duration of the ritual's effect becomes permanent, and the effect will continue even if the Permanence ritual lapses (because the requisite healing surges were not spent). The ritual effect ends only when you lose this feat through retraining.
Notes:
1. Level 3 darkvision might be too low-level. Lighting isn't really an issue (sunrods are cheap), but the advantages for stealth may warrant making this ritual level 5 or 6. Frankly I can't see darkvision being as useful as Raise Dead; it's maybe as useful as Water Breathing.
2. Permanence is a risky idea because of interactions with other rituals. Permanent Weather Control? Permanent Water Breathing? Permanent Silence? Permanent Linked Portal, for crying out loud... These sound powerful but not game-breaking especially compared to some of the other paragon-level rituals.
3. Permanence really isn't, because it requires ongoing healing surge expenditure. This seems to be the way some other rituals work. Often they have a bonus "If you sustain the ritual for a year and a day it becomes permanent" but I felt that maybe that is too strong. Hmm, perhaps a higher-level ritual...?
4. Spending a feat to make a ritual (affecting yourself) truly permanent seems like a reasonable price to pay.
-- 77IM
PS. This took me about a half an hour to do: that seems like a decent amount of effort for most NSFW-type contests (longer ones could be "special events" or something).