eGo vs 808:
eGo is a big battery version with a 510 connector. 3.1 or 3.2V output (I forget what the regulator is set to). 650 mAh or greater capacity per battery. Mainly manual (don't know if they make an auto). Look at liberty-flights -- $40 sale right now, after the 20% discount, if they still have some in stock.
808: A general connector, available in 250 or 380 mAh batteries (standard or what's called XL or Mega); a mini or shorty battery may also be available. Manuals or automatics available (don't let others scare you off of automatic if you would like one -- the 808 autos are decent if you don't completely flood them. Large variants also available (I'm using Greenworld G400 900 mAh from NHaler). 3.7 - 3.8V output = more power for a given resistance atomizer (power is voltage-squared divided by resistance, more = more vapor, more throat hit). NHaler and vapor4life have been where I go -- they have 10% coupon codes (saveinnj and smilin), vapor4life frequently has higher % off -- check their forum. vaporetc also has good 808 pricing, and often has at least a 10% discount.
Standard 808s are a cigarette form factor, with a standard 808 + cartomizer about the length of a 100 cig, while an XL/Mega + carto is about an inch longer.
808s people generally use cartomizers, though I believe a 901 atomizer also fits. eGos you can get either atomizer + cartridge (cart) or cartomizer. Standard 808 resistance is 3 ohms, while some places sell around a 2.6 ohm cartomizer, others sell around a 3.3 ohm (fewer ohms = more power, hotter).
Backwoods Brew and Johnson Creek are popular for tobaccos. Vapor4life has a large selection, I used their Kamel and Wowboy early on. NHaler has some good flavors, too. I've been pretty happy with the samples of juice I've picked up from vaporsetc along with hardware from there.
Generally shipping is a pain, so it's nice to pick up some initial liquid with your kit, couple different flavors and mg (strength, nicotine, in mg/ml or sometimes just called mg). Flavors called RY4 and RY5 are pretty popular. Backwoods Brew Maxboro is pretty good, and their Honey Flue Nut is nice (their malty toffee is super, though not a tobacco flavor).
Good luck!