Like jart says, depending on the turnover of stock at your LFS, it might be worth your while to ask when they get their shipments in. For example, one place near me gets plants in every Tuesday. So if you stop by on a Wednesday, you have your choice. If you stroll in on a Monday, the tanks may look a little bare.
Do you have any idea how you want your tank to end up looking, or do you just want to start off with the thrill of some living green?
I think a safe route is to start off with hardy fast growers. At first, it is a real feeling of accomplishment to have the darn things live and grow. You can start off with something like giant hygro. A really easy plant to grow. At some point you might end up tossing it because it grows too well, but it really gives a sense of success early on. Other than real cheap fast growers, you could spend a couple of extra bucks ($5-6?) on some red sunset hygro for some easy pink color. Maybe another $6 for a red or bronze crypt wendtii for a darker hue, tho it might take a little longer to really establish. You can fit an anubias nana or coffefolia in just about any mature scape, and they are essentially impossible to kill, but they can be really slow growers - especially until established.
So I would go with a sunset hygro and crypt wendtii for color, then stock up on whatever is fast growing, hardy, and cheap. You can have a lot of interest in just the contrast in shade and leaf shape between anarcharis, watersprite, and corkscrew vals. Maybe 5-10 dwarf sags for a little lawn area. And tie some java moss and java fern to your rocks/wood.
Just my opinion.
And don't forget to post pictures!