So I can do leg presses with 650lbs reliably enough and probably more but idk... putting all those 45lbs weights on the leg press machine is a bit of a hassle. Is there any exercise that works legs in the same way without requiring that much weight?
The stimulus that the leg press provides is difficult to replicate for the same reason that it has become a hassle for you, it allows for a lot of weight to be used. As mentioned by Berin, the weight you use for the leg press will greatly differ from the weight used on most other leg exercises. This makes it a hard exercise to replicate in terms of muscle stimulus, however there are many other great exercises to build the same muscles that the leg press builds, the quadriceps, glutes, hamstrings, and calves. Here are 3 of those exercises, along with video demonstrations of them, several research-based tips for getting the most out of them, and alternative ways you could continue to include the leg press in your routine, should you find that you simply need it in your life.
Lunges - As shown by study 1, forward lunges have been found to strengthen and build the quadriceps, hamstrings, and even part of your calf. Done with either a barbell on your back, or holding dumbbells at your side, the lunge can be a great substitute for the leg press. To get a closer look at the exercise performed in action, check out this link
Squats - Most lifters will agree that the barbell back squat is a contender for the title of Most Physically Brutal and Exhausting Exercise Ever. Berin already mentioned squats so I won't talk it about them much more, I'll just leave you with another example video of the exercise being performed:
And I'll mention that when squatting, avoid throwing in the BOSU ball, or any other unstable surface that forces you to balance on top of it. While it makes sense to believe that squatting on an uneven surface would make the exercise even more challenging, rewarding, and even "exciting", it has unsurprisingly been shown (in study 2) to greatly reduce the amount of weight able to be lifted, which is a large contributor to muscle and strength growth. This makes squatting on an uneven surface more suitable for a rehabilitation program, than a strength training program. To mix it up, you could substitute front squats with back squats, as both offer different advantages and stimulus.
Goblet Squat The weight used to perform the goblet squat will be marginal compared to what you use on your leg press, however the goblet squat has the benefits of reinforcing proper squatting form, and is especially helpful if you deal with any ankle, or wrist flexibility problems. And of course, here's the video demonstration.
Hope this helps, and happy leg training!
Squats: Squats are a full body exercise, hitting just about every muscle group. Front squats and Olympic style back squats (high bar, very deep squats) emphasize the quads, while low bar back squats emphasize the glutes and hamstrings more.
You will find that you simply won't be able to handle the same amount of weight on the bar with full range of motion squats as you can with a leg press. One of the reasons is the fact that your core and upper back can become limiting factors. You may be humbled by how little you can squat compared to how much you can leg press at first, but with a good strategy that can be overcome in time.
If your emphasis is with size, stick with higher rep ranges, but make sure you can maintain proper form throughout the sets.