UPDATE: As of December, 2009, Careful Attack has been errataed to add Dexterity or Strength to the damage roll, so my suggested fix for that power is no longer necessary (though I like it more than the official version).
I'll do the usual trick: show modified powers now, then have some discussion after the cut. I'm leaving Beast Mastery for other day, as I think it's a whole different animal (heh). Also, no changes for Nimble Strike -we like you as you are, NS!
This will hurt a little now, but you'll feel much better afterwards...
Ok, we're ready to go!
When it comes to at-will powers, Rangers find themselves in an awkward position. On the one hand, they have Twin Strike, the best at-will in the game (though it's a really close call between that and the cleric's Righteous Brand). On the other hand, and intimately related to the first issue, they hardly ever get to use whatever power they have chosen as a second at-wil. And it's not just Twin Strike to blame, here, as some of the worst at-wills in the game -Careful attack, I'm looking at you- are also sported by rangers. Nevertheless, I think that even without those crappy powers, it would be almost impossible to have a somewhat balanced selection that didn't involve changing Twin Strike.
The way 4E rules are made, powers allowing multiple attacks beat almost anythin, damage-wise. Not only that, but they are more accurate than the so-called "accurate attacks" (poor, poor Careful Attack!), since you're more likely to land an attack when rolling twice than when getting a +2 bonus. Or a +4, for that matter.
The changes shown above try to address the issue, bringing down TS to a more mundane level while improving the subpar choices so that they are actually interesting to use. Note that they imply a significant reduction (between 10% and 20%, from my calculations) to a Ranger's damage at-will damage output. Since Rangers were usually well above most other classes in terms of damage, you could probably just apply these modifications and call it a day. I suggest using them with the feature changes I proposed previously, which increase the damage potential at the cost of making it more rogue-like (and I mean being Sneak Attack-ish, not looking like an '@').
Since I have probably bored you to death with Twin Strike (I'd argue that TS usually has that effect), I should comment on the other two powers. I felt Careful Attack needed some sort of side effect, since hitting often is something that TS was already great at. I settled with a bonus to hit for the following turn, because, if the numbers are right, it could allow for a power rotation: open one turn with Careful Attack, have an enconunter power, or Twin Strike, or whatever the following turn, and repeat. While it may not seem terribly varied, it should be more fun than just using a single attack. Since it was still a bit too weak, extra damage was added. I could have used Wisdom modifier here, but I found that at higher levels it would be almost equivalent to just using the main ability, so I went the halved main ability route.
Regarding Hit and Run, I always considered that it failed on the 'run' part. The added movement should interact nicely with the other effect, and improve the ranger's emphasis on mobility, which is usually one of the most fun aspects of playing a striker. Of course, this really shines with the improved Fighting Style I proposed, but it should work either way. Again, I could have linked the bonus to Wisdom modifier, but I think it plays better when it gives 3-4 squares of movement.
Bonus home rule: Global multiattack adjustment for Rangers
A mere -2 penalty to hit, by itself, isn't really enough to balance multiattack powerhouses like Twin Strike, but it sure helps. If you really feel that your rangers' damage is excessive, or that single attack powers are way below multiattacks, the following modification may be for you:
Whenever a ranger power allows you to make more than one attack on any single target, apply a -2 penalty to hit to that power's attack rolls.
This wouldn't apply to burst powers, or powers that forced you to make all attacks on different targets. Powers that give you the option to hit either a single target or several (such as Twin Strike) would always have the penalty, regardless of how the attacks are assigned. Below, I provide a table with all ranger powers that would take the penalty. (Paragon path powers not included)
It may be hard to believe, but there are a few multiattack powers that could be considered more or less balanced, or even weak. The table below lists what I consider fair powers. It's probably safe to keep these without a penalty: