My most unforgettable team is my emerald team. My blaziken and my friend's dodrio (nicknamed "diglett") kicked butt in double battles, while my Azumarill (named Mar, rose him up from level 4) saved my hide in the elite 4 champion battle. mew is just awesome for any team, and Slaking's *cough*useless*cough* but a tank. the 6th one was a Wailord i named Spout, and that is 1 team i'm never gonna forget.
in W2, last night my team officially became unforgettable. Magnemite, Tepig, Munna, Mareep, Psyduck, and Drifloon helped me catch my first ever SHINY pokemon (level 10 Patrat, caught him in a great ball, replaced Munna with him).
All my other teams had no lasting impact and/or are too weak/unbalanced to mention.