I usually don't like buying at chain stores but do check them out. Sometimes you find some unique deals. Such as finding something you haven't found anywhere else. Sometimes they won't even have it labeled or it'll be mis-labeled and you'll get an incredible deal.
I got 4 gorgeous rainbowfish I haven't seen before for $1.09 each today. They were in a tank with danios. There was no label for them so I got 'em for the price of the danios.
I know what you mean about the plants at Petco. They basically always have those same plants. Last week I actually saw a zebra loach in with the plants and got him for 3.99. He had barely any room in there with all the plants bunched. He's now happily swimming in my 20g with my other zebra loaches.
I got some lace java fern on a piece of driftwood for a good price awhile ago. That's about all I got for cool plants at Petco.
Current fish (includes all 3 running tanks): Polypterids, severums (of which I raised from eggs), gouramis, plecos (gold spot ones & a gurupa), loaches (zebras, yoyos, & a kubotai), macculocchi spotted silver dollars, an African butterfly fish, & Ctenopomas (a leopard & an ansorgii)