Having asked this question myself, I'll answer.
The races you see as lacking often get advantages you miss. Are you playing 1.0X or 1.1 beta 4a? 1.1 beta 4a tweaks some things, but mostly it prevents some races "bonuses" from dissapearing when you hit reset, making it look like they are weaker. Anyway I digress, here is a rundown of why some races aren't underpowered compared to another, and just different.
Terran: Arguably the most contreversial, even I went "WTF?" when all the beginner guides said use them as your first race when it seemed liked every other race was so much shinier ><. The fact is though, their bonuses are quite strong. In Beta 1.1 4a they get a free 25% to diplo and free 25% to trade. Yes the drathi have more then that, but I rather have the 25% trade, depending on the game I am playing, then the bonuses to espionage etc. The second part, is they are the only race to start with Xeno Communications AND a Diplo bonus. In my last game, I rushed to Universal Translators and then the tech that gives diplomatic translators, and I was able to EASILY trade for every tech I was missing, and more. I would do a diplo tech, then a off tech (for trade, because unless I really needed to, I didn't want to give my diplo bonus techs away), and it solidified early relations with me, while keeping me on top tech wise (maybe not leading tech wise, but competitive enough only with a lot of allies.
Iconians: No racial bonuses whatsoever, made me a sad panda, until I played them and found out they have a class 15 (now 14 in beta 1.1 4a) starting planet RIGHT from the start. I took the 3 point green thumb under "planet quality" as my extra bonus, which means in 1.0X they start as a class 17 planet, while in 1.1 beta4a they start as a class 15 again. That game I got so lucky and had a few class 10-14 class planets around, and I just dominated, since the 10% bonus only gets better as you terraform those planets.
Yor: Miniturization bonus, nuff said. Play around with fast teching to early engines, and watch your ships out race everything for a long time.
Other races, just play around with, run through some games with them, if they look weak initially, or gipped "stat" wise, they usually make up for it with a unique tech, starting planet or something. It's all there. If you don't like playing beta's then wait for 1.1 to come out next week, as I said it makes the racial bonuses easier to see, so things that look gimped now don't.
