As everyone should know, Poison Ivy first appeared in Batman #181 (1966) and then #183. What a lot of fans don't realize is that she didn't appear again until #208 (1969). However, this issue was just a reprinting of #181 and part of a compilation of existing stories.
I hate to even acknowledge the following bit of information but after #208 Poison Ivy did not appear in a "regular" comic book for 8 years. She
finally reemerged in Batman #291. Oddly enough, Ivy did appear often in the Batman daily strip during this absence from the monthlies. (The Ledger Syndicate produced these dailies.)
The featured strip is a three panel piece featuring Poison Ivy and Batgirl having a bit of hand to hand combat under the moonlight. This originally appeared in papers on August 30th, 1971. With contributions from Al Plastino (art) and E. Nelson Bridwell (story). Nick Cardy was also a regularly featured artist.
There's a few of these floating around the internet and I plan on featuring all the daily strips (available) with Poison Ivy.
Addendum: As Aaron Severson pointed out in the comments section - Poison Ivy did have a few cameos in non-Batman related titles (up until September of 1977). Beginning in 1978, Ivy would return to the tried and true monthlies. Below are some of the mentioned titles with a few other appearances. Also, the following panel is from Ivy's first apparance in "Superman's Girlfriend Lois Lane" (#115). Lovely huh?
Superman's Girlfriend Lois Lane, 115, Oct-71 "Computed to Kill Pt. I" (cameo, last panel)
Superman's Girlfriend Lois Lane, 116, Nov-71 "Computed to Kill Pt. 2" (extended cameo in backup story)
Secret Origins: Supervillains, 39, Oct/Nov-75, (Limited Collectors' Edition presents - only appears in villains poster)
Superfriends, 1, Nov-76, "The Fury of the Superfoes" (cover)
Superfriends, 2, Dec-76, "Trapped by the Superfoes"
Batman, 291, Sep-77, "Where Were You the Night Batman Was Killed?" (cover - brief cameo)
Batman, 292, Oct-77, "Testimony of the Riddler" (continuation of prior issue - breif cameo, non-speaking role)
Batman, 293, Nov-77, "The Testimony of Luthor" (continuation of prior issue - brief cameo)
Batman, 293, Dec-77, "Testimony of The Joker" (continuation of prior issue - brief cameo, non-speaking role)
Secret Society of Super-Villains, 10, Oct-77, "Triumph and Treachery" (cameo - last page only)
Secret Society of Super-Villains Special, 6, 1977, "Death Times Five" (DC Special Series - DC Giant - extended cameo)
Justice League of America, 158, Sep-78, "The Super-power of Negative Thinking!" (cover - extended cameo)
Batman Family, The (Dollar Comics), 17, Apr/May-78, "Horoscopes of Crime!" (second story - extended cameo)
World's Finest (Dollar Comics), 251, Jun/Jul-78, "A Kiss of Death Times Three" (fifth story - extended cameo)
World's Finest (Dollar Comics), 252, Aug/Sep-78 (part 2 of previous storyline - see above - extended cameo)