Flight is a powerful ability to give to PCs right off the bat; there's a reason the Fly spell was split into weaker versions in the 3.5 Revision, and still 3rd-level or higher spells. It usually bypasses the need for skills like Balance, Climb, Jump, and sometimes even Swim or Tumble. Only in places with intense winds or magically messed-up gravity is flight a poor option compared to these skills. Being able to fly allows the bypassing of many encounters, enemies, traps, plot hooks, obstacles, and so on, not to mention providing easy travel; no need to slog through the marshes or hack your way through the dark forest or tall grasses, just fly over it all and avoid the delay/plot hook/ambush/whatever.
Aarakocra from Monsters of Faerun are likely about the weakest, intelligent flying race you could use, and I don't even have an ECL for them; they have 1 hit die and only a few minor racial traits, yet even they are probably ECL +2 or ECL +3 (perhaps Player's Guide to Faerun addresses this in 3.5, but I wouldn't know). The Winged Creature template from Savage Species grants a +2 Level Adjustment in exchange for +4 Dex, +2 Wis, and flight. The fly speed it grants is greater than the creature's base speed, and the manueverability is based on the creature's Dexterity score. A custom, diminished version of the template might give simply a Fly speed of 20 feet with Poor maneuverability, probably not even that much, for a +1 Level Adjustment instead of +2.
My suggestion in case you are really dead-set on making an ECL+0 playable race with flight, would be something as follows. Small humanoids with wings, -2 Strength and +2 Dexterity as usual for a small critter, base speed of 20 feet, a specific favored class, maybe a +2 racial bonus on some skill to represent the slightest of cultural inclinations or something, and no other racial traits except for flight with wings. Make them essentially winged halflings or something, but without the various racial traits of halflings. Give them a Fly speed of 20 feet, Poor maneuverability, and limit them to no more than 1 hour of flight during any given 3-hour period, incurring 30 minutes of fatigue after a total of 30 minutes worth of flight during any such period, and a further 30 minutes of fatigue or maybe exhaustion after another 30 minutes worth of total flight time during any given 3-hour period. Even this may be too powerful for an ECL+0 race, but at least it would be reasonably close. Maybe require these 'flying halflings' to attempt a Constitution check after every 1 or maybe 10 minutes of flight during any given 3-hour period, increasing the base DC of 10 by +1 after each check, resetting the DC to 10 after that 3-hour period. Maybe even have their wings replace their arms, such that the midway point on each wing has a hand that is unusable during flight.