Yay, first GE card review! Good thing too with prereleases only 2 weeks away.
Anyways, Togekiss is a great card if you can get it out early to mid game. It's Poke-Power, Serene Grace, lets you (once when you evolve Togekiss from your hand to the Pokemon) to pick up the top 10 cards of your deck, choose any Basic Energies you find and attach them to any of your Pokemon in any way you like. Then you put the other cards back onto your deck and shuffle. This is almost hands-down one of the best options for Energy acceleration in this format. On average, you'll usually find at least enough basic energy to power up one Pokemon completely (of course, this is all dependent on how many basic energy you play). Togekiss can be combined with just about any deck simply due to this Power, but two deck that definately takes advantage of this are Garchomp and Blissey. Garchomp, in particular, requires usually about 3 turns to power up with the correct energy. But with Togekiss, you have access to a possible flood of different energy types that you need. Blissey likes Togekiss for the obvious reason; its sole attack does more damage when there is more energy on her.
Stat-wise, Togekiss is average. 120 HP is solid for a Stage 2, +30 Weakness to Lightning could hurt is Electivire shows up, -20 Resistence to Fighting helps in Lucario match-ups, and 1 Retreat Cost is actually pretty cheap. Its attack, Air Scroll, deals a solid 40, but with a flip of Heads, can deal 70. And even if you flip Tails, then you heal 3 damage. So Togekiss is not just a one-time deal; it is actually quite a potent attacker and staller.
Modified - 9/10 (A good many decks will be using it for energy acceleration, and even those that don't will be tempted to try Togekiss)
Limited - 10/10 (If you can get this out and have some decent Pokemon on the bench, your opponent may as well just forfeit. Limited decks usually have lots of Energy in them, meaning you can usually power up most of your Pokemon in one go. Togekiss as an attacker is also great)
Unlimited - 3/10 (I think that if you can get it out quickly enough and get enough energy onto your Pokemon, SER won't hit you as hard)