I've been doing the 5/3/1 program by Jim Wendler for about 2 months now, and I plan on sticking to it for a VERY long time.
In short, you take your 1RM, and you work in "waves" and "cycles". A "wave" is just going through each of the 4 days - squat day, bench day, deadlift day, and OH press day. Once you have went through each of the 4 days, then the wave is completed. A "cycle" is going through 4 waves, where each wave is progressively harder then the previous one for the first 3, and the 4th one is a deload. For a detailed explanation of the 5/3/1 program, do a search on google, and you'll find tons of write-ups on it. This is just a review of why I think it's such an awesome program!
I love this program for several reasons:
1.) It is very versitile. Aside from the "5/3/1" lift which is bascially set in stone, the assistance exercises can be mixed, matched, changed, and varied in any way you like. I have been getting kind of bored with "cookie cutter" routines such as starting strength, or Madcow's 5x5 (which are both EXCELLENT routines BTW, and all beginners should do them before moving onto anything else). I was just sick of going into the gym knowing that I would be doing the same damn lifts day in and day out. The only thing that was changing was the weight. Now, while this is really the #1 most important thing IMO (increasing the weight in the main lifts), it just gets boring doing the same exercises for the same set and rep schemes for years and years.
I believe everyone should bite the bullet when they are new and start out the "boring way" just so they can get thier lifts up in the most efficient manner, but after you reach the point where you can't add weight to the bar at least every week, then something more advanced like this can be used. In other words this is NOT a beginner routine (although beginners could do it, but it would not be as effictive and efficient as starting strength).
2.) The "5/3/1" lift. This is the part that remains the same, and it's the most important part of the program. You do either the squat, bench, deadlift, or overhead press (depending what day you are on) for the designated percentage which is based off your 1RM (this "1RM" increases every cycle). Every program should be based around increasing the amount of weight you are able to use on these main lifts. The 5/3/1 is simply just a periodized, percentage-based way of increasing these lifts over time. So while in #1, I said this program is very versitile with the assistance lifts, the 5/3/1 gets the necessary stuff done. The progression is a bit slower then what I'm used to, because you only increase your 1RM based percentages every month BUT it's done in a much more intersting way then simply progressing linearly every week.
3.) The "All out rep max lift". This is the really fun part! Each day, whether it's OH press day, squat day, deadlift day, or bench day has set goals to it (wave 1 is 5, 5, 5 at 65%, 75%, and 85%, wave 2 is 3, 3, 3 at 70%, 80%, and 90%, and wave 3 is 5, 3, 1 at 75%, 85%, and 95%). So if you hit your goals for the day, great! That's what you're AT LEAST supposed to do. BUT, for the last set of the main lift each day, you're supposed to go for an "all out rep max". For instance, if you're on wave 2 and it's squat day, and your last set has you doing 255 lbs., that means you're AT LEAST supposed to be doing 255 lbs. for 3 reps, BUT if you can do more, you should. For instance, today is squat day for me, and I'm on wave 3, and my final set of squats is simply 1 rep @ 255 lbs., but I'm looking forward to seeing how many reps I can get, because I know I can do more then just 1 rep. The most I've ever done with 255 was 10 reps, today I'll shoot for more then that. This is the really fun part.
As time goes on, and the "1RM" keeps increasing each cycle, going for 10+ reps simply won't be possible anymore, but the cool thing about this is that every cycle is just SLIGHTLY heavier then the previous cycle. So within 2 years, if I'm repping 405+ lbs. I won't be suprised.
4.) This program is the perfect mix of "powerlifting" and "bodybuilding" into what some people have called "powerbuilding". The "5/3/1" lift has you working from percentages based off your 1RM which keeps increasing, just as a typical powerlifting program would have you do. Yet that "all out rep max" last set, and the varying set/rep schemes with the assistance lifts are more like bodybuilding training giving you the high volume and "pump".
All in all this program can be used to build some serious f***ing size depending on the volume you choose to use with the assistance lifts, and the strength gains are slow yet steady - I don't see myself stalling in my lifts and needing a reset for at least a year by training this way.
So after you have gotten all the newbie gains you can from something like Starting strength, and you just simply can't keep adding weight to the bar every single workout or even every single week, OR you just wanna slow down the pace at which you are increasing your lifts, this may be the way to go.
As I said, the assistance lifts are entirely up to you, and can be used for any set/rep scheme you'd like. I superset a lot of stuff with no rest because it's great for conditioning, and it saves time too. Wendler has some suggestions in his book, but the only thing that is set in stone is the "5/3/1" lift each day. For the last 2 months each of my days has been:
Squat day- 5/3/1 bulgarian split squat
hack squat
dragon flags
hanging leg raise
Bench day - 5/3/1 Incline DB bench
pull-ups/chin-ups
lateral raises
Deadlift day - 5/3/1 front squats
good mornings
weighted decline situps
hanging leg raises
OH Press day - 5/3/1 power cleans/clean & press
barbell rows
close grip bench press
curls
Here is a cool little calculator thing that I made on excel that figures out the weights to use just simply by entering in your 1RM for each lift:
http://www.sendspace.com/file/7u4b20 Fun stuff!