Two of the best +1 LA templates have already been named - Feral and Mineral Warrior. They are absolutely underpriced for what they get. One more that's great for casters (at least sorcerers) is the White Dragonspawn from the Dragonlance campaign setting. +7 natural armor, fly speed, a breath weapon, +2 bonus to dex and con, and
+1 level of sorcerer spellcasting, darkvision, and some other stuff I can't remember at the moment make them a heck of a grab at only +1 LA.
Half-Fey from the Fiend Folio is also pretty nice, but it's a +2 LA. Feytouched from that book may be worth the +1 LA it has, depending on what you're looking for.
Chaos Gnomes from RoS are probably worth the +1 LA, though they work best for casters and it's usually a bad idea to have LA with casters (the exception being the white dragonspawn mentioned above). Whisper gnomes from that book are worth a +1 LA, but they actually don't have one at all!
Necropolitans (Libris Mortis) don't have a LA, but you lose a character level when becoming one. If done early in one's career, this is a super cheap cost to become an undead.
For creatures that have a low LA but also some racial HD, I like some of the following (I know the OP said no racial HD, but they're worth keeping in mind anyway):
- Marrulurk (Sandstorm): +2 Str, +6 Dex, +4 Con, +6 Wis, +4 Cha, Point Bland and Rapid Shot as bonus racial feats, death attack, +2d6 sneak attack, and some other goodies for 3 HD and +1 LA...sign me up!
- Sylph (MM II): 3 Outsider HD and +5 LA, but they cast spells as a 7th Level Sorcerers, plus they get all kinds of good stat boosts and at will improved invisibility. Plus, for every HD they gain, they gain a level of sorcerer spellcasting, which with a strict reading of the rules means they can advance in a class like rogue and still improved their casting!
- Varoot Nerra (Fiend Folio): 1 HD and +3 LA, but they have good ability adjustments and reflective spell resistance is absolutely OMG.
There are others that have higher ECLs like ethergaunts, sharn, skullcrusher ogres, etc., but I doubt you're interested in those.