There are few other possible entry arrangements that drift to mind. Here are two involving a zip and one (failed) tension-based one. I wouldn't recommend them as strongly as the other neckline options.
Sew zips into raglan sleeve darts, with suitable collar neckline.
This is functional, but the zip ribbon is a little scratchy on the suit I made, and since zips don't stretch it wrinkles significantly along the dart when I raise my arm (because I stretched the fabric when I sewed it in). I think I can work around the scratchiness by using the correct length of zip, by taking it out of the plastic packaging more carefully, and/or by covering the zip inside the suit with some spare suit fabric.
I've also made a zentai suit (catsuit with integrated hood) with shoulder zips, and it works pretty well: the shoulder zips twist (gently) at the base of the side of the neck and around the back, where they meet the zip running down the back of the hood in an inverted T-shape. The sewing is a little tricky, although this suit has less puckering because I didn't stretch the fabric when I sewed the zips in, and it doesn't need special reinforcement as I thought it would because you can sew the zip ribbons to each other at the end.
Inside leg zips
Sew zips into the inside leg seams.
I wouldn't recommend this as an entry option for tight suits: with zips that reached my knees (12"), I had quite a struggle getting out of the suit and burst a few stitches in the process (despite being fairly flexible). It was even harder getting in, and particularly hard to pull the zip tabs up (partly due to having to pull the edges together). The zips also wrinkled along my legs - my overestimate of the amount the fabric would stretch - but that's difficult to get right, and is therefore likely to happen.
Had the suit been looser, or zips reached the tops of my calfs (16") it would have been easier.
...but as a fly...
Caveats aside, a horizontal fly in the inside leg seam would probably work. As with the shoulder dart zips, the zip ribbon could be itchy against sensitive skin, and it would seem advisable to sew additional fabric over the zip as a shield.
If you do add it as a fly, I would suggest sewing a single zip across the crotch point, rather than two zips meeting at the crotch point, and bar-tacking the opening end of the zip permanently closed.
This seems a bit pointless unless colour-blocking gives you a seam to follow. It would give the suit an asymmetric stretch which at worst might draw you into poor posture, and at best would probably feel odd (but you might like that).
This just won't work: from hip to underarm, I'm 15". Twice that is 30" which isn't enough to fit around my 40" waist. Even if I were skinny with a 30" waist, there's still no excess for wriggling into the suit. Too bad.
Perhaps if the side seam were hook-and-eye or pop-stud, and thereby able to stretch, this might work, but I remain suspicious about getting in sideways through a 30" slit.
I thought it might be possible to get into a suit through a couple of half waistbands, both at the back: one attached to the 'trouser' part and one to the 'top' part, and overlapping (a little like the 'wrist escapes' I mention in the gloves section). It is, but you have to bend double to get both halves of yourself in, and even if you want the suit only moderately tight, the two half-waists open up (or feel like they're about to open up) like a recalcitrant Tshirt untucking itself, and things are just drafty. If you make the overlap deep enough to fix that, it's very hard to get in. So... sadly, I wouldn't count this as a practical solution unless you have peculiar requirements that I don't think I want to think about.