Let's see, CRs appropriate for each spell level..... I'm going off the 3.0 versions here, as I don't have a 3.5 MM and PH to reference. I know that the CRs don't match up to spell level, though. Also, keep in mind that the creature type and special abilities may affect whether or not a creature should be summonable, and at what level.
Summon Monster I has critters of CR 1/3 to CR 1/2, plus templates added which probably make them almost CR each (but not quite). Something of CR 1 might just barely be fair for the SA 1 list.
SM 2 has critters of CR 1/2 to CR 1. Many have a minor template, so each is around CR 1 but not quite CR 2. So anything not quite worthy of CR 2 could go on the SA 2 list.
SM 3 has critters of CR 1/2 to CR 4 (the triton really doesn't seem worthy to be CR 4 though, so that's probably a fluke). The vast majority are CR 2 with a minor template. The CR 1/2 fiendish small viper is probably here because it has poison that deals Constitution damage. CR 2 creatures and those of up to CR 2 with a minor template should be fine. Most likely, anything of CR 3 that has no significant special abilities (no regeneration, spells, teleportation, etc.) might be fine in the SA 3 list.
SM 4 has critters of CR 1 to CR 3. The only CR 1 is the fiendish medium viper, for the same reasons as its smaller cousin being on the SM 3 list. The majority of these critters are CR 2 with significant special abilities that may be useful to PCs, or just CR 2 with a template added, and a few are CR 3 with minor or moderate special abilities. The giant eagle and giant owl are probably here because they can serve as short-lived flying mounts to PCs, being such large flying critters.
SM 5 has critters from CR 2 to CR 5. The fiendish large viper and fiendish large shark are the only CR 2s here. Most creatures here are CR 4 with a minor template. There are also a decent number of CR 5 creatures here. Mephits and medium elementals are here at CR 3 with their various kinds of special abilities. As are the CR 3 quasit and yeth hound, which have some potentially useful special abilities. I dunno why the CR 3 formian warrior is here, or the pegasus (probably more appropriate for SM 4).
SM 6 has critters of CR 3 to CR 7, averaging CR 6. Most are CR 6 or 7 it seems, with a few CR 5s, I think one CR 4 and two CR 3.
SM 7 has critters of CR 5 to 9, mostly around CR 8 and 9. Just a few are below CR 7, and there are some three or four of CR 7.
SM 8 has critters of CR 4 to CR 10. Most are CR 9 or 10. The janni is here at CR 4 for some reason; it has the same ability to plane shift itself and other creatures that a djinni has (which is on the SM 7 list). I guess the barghest is here for the same reason; somehow the designers thought its special abilities weren't appropriate for a lower list.
SM 9 has critters from CR 5 to 14. Dunno why the greater barghest and the nightmare are here at CR 5, and the xill at CR 6. The rest are CR 8 to 14, mostly CR 9 to 11.