Writing down my notes from a trip last month, because the memory is already fading:
Les Pilliers: hard to miss, but really, really good Italian food--fantastic tomatoes, and very good ravioli. Expensive (mains around 5000 CFA or so). Thanks to the person on this board who mentioned it.
Le Gourmet (something like that): right on the plaza with the mosquee. Simple, local-looking place with a big chalkboard menu, most of which actually seemed available. A truly excellent red sauce for couscous -- not sure what kind, it was just listed as generic sauce -- very multi-dimensional and rich. Very good fresh salads (carrot and I forget what else), and a huge fluffy omelet with potatoes. Nice, albeit quiet, man in charge. Slow service, of course. Recommended.
Le Palmier: may be forgetting the name--it's the Algerian place on the Airport road, listed in Lonely Planet, with some tables on a patio out front. Really good lamb shank, with generous use of lemon and parsley. Not as good as Le Gourmet, but still good.
I didn't end up eating anything other than breakfast at my hotel, Auberge d'Azel, but it's such a gorgeous setting that I'd recommend checking it out if you want/can afford an upscale meal.
Had two GREAT meals at Maquis "Watta", near the Grand Hotel. Small-ish maquis, sweet, friendly staff. The poulet yassa and sauce feuilles both had excellent depth of flavor, and very big portions. Sauce d'aubergines came with two fantastically flavored chili sauces--a fresh green one, and a fabulously smoky red. I didn't love the aubergine sauce so much (wasn't bad, I just didn't think special), but my friend did. I can't remember the address, but it was right around the corner from the Hotel Terminus. From Hotel Terminus, turn right (on the street that leads you to the Grand); turn right at the next intersection; and the maquis is on the right, with a huge yellow Maggi seasoning sign.
Not very impressed by the Chinese/Vietnamese place--Golden Dragon, I think? Nice big space and very refreshing to see lemongrass on the menu, but it was just basic gloopy stir-fries, nothing special. Small portions, if you're hungry, and no chicken was available at the time (right when the bird flu news hit, so some places got skittish). Not a bad change if you've been on the road for a while, but don't get your hopes up.
Not too much food was available at stops between these two towns that time of year: some sweet rolls and that very stiff fat-backed dried meat, which I decided to forego, and that was about it except for some excellent steamed yams in Tahoua, and further south, it was mango season.
Out in the Tenere for two weeks with a few Toyotas, we twice bought animals--a goat and a sheep--and slaughtered and roasted them for dinner. Completely different taste to the lamb than it has here in the US--extremely delicate and mild, which I had not expected. The goat was tough, of course, and a little stronger in flavor. Local goat cheese also didn't have that familiar taste--instead it was a very fresh milk, dairy taste, more like a young ricotta but with the texture of pressed tofu. Otherwise, even in Dirkou, very little fresh food (no surprise) in the marche--onions, peanuts, a few tomatoes and old cabbages.
I'll take a decent maquis over any other pretender in Niamey, even that hyped Italian grotto place and Babylos. Maquis 2005 is my place of choice (across the bridge), but I also like the famous dibiterie next to the Hotel Terminus, and the brochettes on the patio at the Grand Hotel do not disappoint. Outside of Niamey, I live on kilichi (the dried beef) and a grilled pintade here and there.