I've been doing Starting Strength for a month now and am still progressing fine. However, I'd have time to lift every weekday, and really want to. Is there a similar, well-tested program that I could switch to?
I suppose trying to make my own would just end in disaster.
Rest is as important to your progress as the exercising itself (if not more). If you added in any extra workouts you'll just compromise your progress. This is even emphasized by Rippetoe in the book.
It doesn't matter how much time you can invest, there's simply no point to it. Your body grows muscles while you're resting, as long as there's a sufficient impulse. Maintaining that impulse does not require a lot of time.
The reason many strength programs are not 5-day programs is not because most people don't have enough time, but because it can actually be more effective to train less. And I do not mean more effective per time investment (that would be more efficient), but more effective overall.
When you train what you do is you strain your muscles to the extent that your body needs to repair them (just like a small wound). This repair process overcompensates so that your muscles are larger and stronger than before. The repair process is what grows your muscles, and it takes several days. Now of course you don't have to wait for the repair to finish completely (otherwise you couldn't train more than once a week or so), but you need to wait long enough to make sure that muscle growth is maximized. If you continue to damage your muscles too early during the repair, you risk losing strength instead of gaining it, and your risk of injury increases.
Make sure you don't add lifting workouts just to feel like you're staying busy. The point is to actually make progress, not to do busy work. Investing more time in strength training will take time away from the real thing giving you progress: rest. You don't get strong by working out, you get strong by recovering after working out.
At the moment, a month into the program, I bet you're feeling underworked. That will change drastically if you follow the program and keep adding weight to the bar every workout. That's when you'll understand why it has three weekly workouts and not five.
That said, a three-day-a-week lifting program can easily be made into a better version of itself by going to the gym on one or more rest days. Those additional gym visits should be spent on active rest and mobility.
For example, if you're doing Starting Strength on Monday, Wednesday, and Friday, you could definitely hit the gym on Tuesday and Thursday with something like this plan:
I sincerely hope no-one reading these answers in the future get's the wrong idea here. Hence I feel the need, four years after the original asker was here, to add some context.
Starting Strength is designed to add maximal strength as quickly as possible whilst not specifically building hypertrophy or work capacity. It does this very well and if that's what you want do it but stick precisely to the program, it works. FYI the program lasts no longer than a month or three for most people.
What it doesn't do for the average person is build a nice physique, or prepare you for the best strength progress in your future lifting career. It's very much a one-trick pony.
If you want to be better, be stronger, and look better than the average person who wants a bit of strength, you would be well advised to do a lot more work. Build yourself a base of work capacity, and focus on the one aspect of your training career that anyone aiming for maximal strength or maximal muscle should be focusing on: building muscle mass.
All these answers above about how the three day setup in starting strength is somehow better or more effective are correct ONLY if your goal is as much immediate strength as possible in the next few months, and you don't care about slowing down your long term strength and physique potential by having to backtrack and work on building a base later on once those beginner gains die and you are left stalling like a grounded whale.
tl, dr; if you feel you can do more and you want to actually make long term progress, then please do what your brain is telling you and do more.
If anyone wants further advice, how to build more work capacity, how to set up a routine to do more work etc, feel free to ask.
Edit addition:
http://strengtheory.com/complete-strength-training-guide/ Check the link in that article to download the complete package of programs, which has a well laid out beginners program that has you training 4 days a week and doing 4 main lifts (S/B/D/OHP) in each session plus accessories. If you want to do more, here you go.
And through that link you'll find a powerlifting world record holder's informed take on how to master your training career to get as strong and as big as possible. Covers beginners, intermediates and advanced.
To anyone confused by my views, this should be an interesting read. Hope it's enlightening.
This one here is another awesome program and just so happens to be Mon - Fri: http://www.powerliftingtowin.com/forums/viewtopic.php?f=14&t=1726
If you're a novice, I recommend my other answer, to wit: keep doing orthodox Starting Strength. But there is an alternative.
Normally used only in Olympic lifting programs (snatch and clean & jerk), Bulgarian programming is designed for working out every day, usually multiple times a day. They work only with very heavy weights and use very few exercises. It requires a lot of dedication and I don't think it's normally recommended for novices.
