Oilers' ex-GM (and coach and President) Glen Sather made a number of great trades back in the day. He also did remarkably well in the early days of the free-agency era, when the Oilers could no longer afford to pay top players:
1979 -- Oilers trade Joe Micheletti to St.Louis for Tom Roulston and Risto Siltanen. Joe Micheletti scores 11 career goals, while Siltanen has back-to-back 53 and 63-point (in 63 games) seasons on defence, while even more importantly translating and teaching Jari Kurri. Roulston had a short career, but still scored three times the goals for Edmonton that Joe Micheletti scored in his career.
1981 -- Oilers trade the Pats: Pat Price to Pittsburgh for Pat Hughes. Price goes on to score 16 more career goals for four teams, while Hughes is a regular on the early Cup-era Oilers, scoring 86 goals in 3.5 seasons.
1981 -- Oilers trade the rights to Don Murdoch to Minnesota for defenceman Don Jackson. Murdoch then goes to Detroit, plays 49 more career games and is done (partly due to substance-abuse related issues). Jackson plays 266 games for Edmonton, contributing to two Cup teams.
1985 -- Oilers trade goalie Gilles Meloche (who never played a game for them) for Marty McSorley. Meloche, 35, plays most of three seasons for Pittsburgh and retires. McSorley plays 206 games for Edmonton, winning two Cups, before becoming part of the Gretzky farce.
As if McSorley wasn't enough, the Oilers later (in 1986) acquire Craig Muni from Pittsburgh to complete the Meloche deal. Muni, who (amazingly) wasn't good enough for the mid-80s' Leafs, according to their "brain"trust, then goes +50 his first year in Edmonton, helping the team win three Cups.
(In 1985, the Oilers also sign Craig MacTavish as a free agent, so they lost nothing for him. MacTavish plays 701 games for the Oilers [331 points], serves as team captain, wins three Stanley Cups, and later coaches the team for eight seasons [seven with a winning record], including a conference championship.)
1987 -- Oilers acquire Kent Nilsson from Minnesota for "cash" (I don't know how much, but presumably not a lot). Nilsson scores 17 points in 17 games, 19 points in the playoffs, and wins the Stanley Cup with them.
1987 -- As part of a 7-player deal, the Oilers acquire Craig Simpson for Paul Coffey, whom they are forced (by economics) to trade. This is a good trade for both franchises, who will go on to win 3 of the next 4 Stanley Cups, involving both players. Simpson immediately scores 56 goals and later leads the 1990 playoffs in scoring (his career was cut very short by injuries).
1988 -- Oilers acquire Bill Ranford and Geoff Courtnall for Andy Moog, who also demanded to be traded. Courtnall was in the latter-stages of a 36-goal season (they unfortunately let him go that summer for nearly nothing, just before Sather found out about the Gretzky trade!). Ranford soon became the club's #1 goalie, and beat Moog in the 1990 Final, winning the Conn Smythe.
1989 -- Oilers acquire Norm MacIver from Hartford for Jim Ennis (five career games). MacIver has a 40-points-in-57-games season on defence, before they lose him to Ottawa on waivers.
1989 -- Jimmy Carson refuses to play for Edmonton. Sather trades him (and tough guy Kevin McLelland, who was basically done) to Detroit for Adam Graves, Petr Klima, Joe Murphy, and Jeff Sharples. Those first three form an entire new line for the team, giving them the depth to win the 1990 Cup. (The Oilers then lost Adam Graves for nothing, due to salary-problems as usual.)
The Oilers later send Sharples -- who never played another game -- to Jersey for Reijo Ruotsalainen, who scores 8 points in 10 games, then 13 more points in the playoffs (+13) and helps them win the '90 Cup.
1991 -- The Oilers acquire Vincent Damphousse and Luke Richardson (and two other minor players) for Glenn Anderson, Grant Fuhr, and Craig Berube. Fuhr struggles for years in Toronto and Buffalo and L.A. (before his revival in St.Louis), and Anderson has only one more 20-goal season. Damphousse leads the Oilers in scoring before he, too, tells them he's leaving. Richardson plays 436 games for Edmonton before, as usual, they lose him due to money (Philly signs him), and he plays until 2009.
The trades become more hit-and-miss from around 1992, and most are done simply because the Oilers can't afford to pay anyone (for example, Tikkanen for Doug Weight, though that worked out pretty well).
If only Peter Chiarelli had been taking notes....