For people who play or have tried Castles & Crusades, they will know of the mechanic TLG has termed the 'Siege Engine'. This pretty much unifies within a d20 type game saving throws and skill checks together and functions primarily with the designation of a couple of key attributes as 'Primary'. When rolling a check, you effectively get a +6 bonus if the skill or save is associated with an attribute which happens to be prime. On top of this, you account for a level bonus and any attribute bonus when applicable. The system doesn't do 'opposed rolls' and the modifiers to the difficulty are usually determined by the HD or level of the opponent Pretty simple and a lot of people like it (I do) but some have their issues with the system.
The reason I bring this up is because I recently had the privilege at looking at an alternative that tries to address a couple of problems which people have had in the past with the Siege mechanic. Josh Sherrer, who also uses the handle of 'Julian Grimm', has put together a document for an alternative which has a lot of merit. Early on, I had expressed an interest in this work and he has been kind enough to provide me with earlier drafts which I was happy to give some feedback on. Now, he's about ready to release a 'playtest' version of this and once available, I'll be sure to provide a link here. Of course, you can also check out his gaming blog, HERE. Now, I was interested as both a fan of C&C as well as someone who is also looking at alternative skill/resolution systems for my own games. Josh's system is nice and simple and easily adaptable for C&C or other game one may prefer.
As far as the system goes, it also does not rely on opposed rolls but instead of having a myriad of different 'potential' target numbers, you basically have only four (he refers to it as the '4 Step' system). These are basically difficulty levels and go from Easy to Very Difficult. As a GM, he selects the appropriate level (tweaks it if necessary) and that's pretty much it. This is best for 'situational' challenges but if you need to factor in level or HD of the opponent, guidelines are given for that as well. If you are a wizard trying to do an 'un-wizardly' thing (in other words, the wizard thinks he's the world's greatest thief), then the difficulty gets bumped an extra level. If it's a really easy task... JUST PUT THOSE DICE DOWN (no roll necessary).
It's that simple and elegant as a result.
As far as saving throws go, you can do much the same and he suggests a couple of options ... a three save model similar to what D&D 3.x introduced (Fortitude, Reflex, Will) or a two save model (Mental and Physical).
The drafts I looked at also presents a couple of other optional components which just helps round this out as an alternative system but all in all, it's worth checking out if you happen to find the Siege system (or whatever system your preferred game uses) not exactly to your liking. Check back for an update once links are available.